Boston scored 20 of the game's first 25 points and held a comfortable lead the rest of the way to cut the series deficit to 3-2.
The Celtics will try to prolong their season again when the series moves back to Miami for Game 6 on Saturday.
They are two wins away from becoming the first team in NBA history to rally from a 3-0 deficit in a best-of-seven series after 150 previous teams failed to do so.
Marcus Smart had 23 points and Jayson Tatum and Jaylen Brown added 21 apiece in Boston's second consecutive strong shooting performance.
The Celtics shot over 50 percent from the field and were 16 of 39 from 3-point range, including White going 6 of 8.
Boston are 34 of 84 from deep the past two games after going 31 for 106 in the first three games of the series.
Duncan Robinson led Miami with 18 points off the bench, while Jimmy Butler was held to 14 - his lowest total of the postseason.
The Heat committed 10 first-half turnovers and trailed 61-44 at the break.
Miami point guard Gabe Vincent sat out with a sprained left ankle and was replaced in the starting lineup by Kyle Lowry, who had five points and four turnovers in 30 minutes.
In the latest edition of the league's most decorated rivalry, James was a man on a mission, finishing 15-of-30 from the field, six-of-12 from deep and five-of-six from the free throw line as the only Lakers player to score more than 16.
He added nine rebounds and eight assists, and he should have been awarded potential game-winning free throws after he was clearly hit on the arm while driving for a layup with under a second remaining in regulation.
But the Celtics got the call in Boston, and it would be Jaylen Brown stepping up in the extra period to deliver a win for the home fans.
Brown scored 11 of his team-high 37 points in overtime, finishing 13-of-23 from the field with nine rebounds, picking up the slack for team-mate and MVP candidate Jayson Tatum.
Tatum had a respectable stat line of 30 points, 11 rebounds, four assists and two steals, but he shot a dismal eight-of-25 from the field, while Sixth Man of the Year contender Malcolm Brodgon chipped in a game-changing 25 points (eight-of-15), six rebounds, four assists and two steals off the bench.
For the Lakers, it was Anthony Davis' second game back after five-and-a-half weeks on the sideline dealing with a foot injury, and he came off the bench again for 16 points (six-of-15), 10 rebounds and four assists in 34 minutes.
The win snapped a three-game losing streak for the Celtics, and improved their league-leading record to 36-15.
The Lakers fell to 23-27, and although they sit 13th in the Western Conference, they are only three games behind the Minnesota Timberwolves in the sixth seed.
Clippers extend winning streak to five
The Los Angeles Clippers are enjoying their longest winning streak of the season after making it five in a row with Saturday's 120-113 victory against the Atlanta Hawks.
The Clippers were led by their resurgent two-time NBA Finals MVP Kawhi Leonard, who scored a game-high 32 points on 12-of-20 shooting while adding eight rebounds and four assists.
There were fears Leonard's prime had been stolen from him by injuries after scoring a total of 50 points in his first five games of this campaign, but over his past 10 fixtures he sits eighth overall in points per game at 29.3.
Over that span he is shooting 55.6 per cent from the field, 47.2 per cent from deep and 92.5 per cent from the free throw line while adding 7.0 rebounds, 3.8 assists and 1.9 steals per game, improving the Clippers' record to 28-24.
Kyrie stays red-hot in New York showdown
Brooklyn Nets guard Kyrie Irving posted his sixth consecutive game with at least 30 points and six assists to defeat the New York Knicks 122-115 at home.
Irving, who was named an All-Star starter mid-week, scored a game-high 32 points on 12-of-27 shooting with nine assists, six rebounds and two steals.
Over his past six games, his 36.3 points per game is eclipsed only by Portland Trail Blazers icon Damian Lillard (38.3), while Irving's 7.8 assists would also be a new career-high as he shoulders a massive workload in the absence of injured superstar Kevin Durant.
The Celtics led by as much as 45 points and benched MVP candidate Jayson Tatum in the fourth quarter, in a game where the Suns welcomed back All-Star Chris Paul from a heel injury.
Tatum finished with 25 points with five rebounds, two assists and two steals. The 24-year-old is the first player in Celtics history to average 30 points per game in his first 25 games of any season.
Jaylen Brown also scored 25 points with seven rebounds, while Malcolm Brogdon added 16 points off the bench.
Boston led 69-42 at half-time in the blowout win, which was the Celtics' second-biggest margin this season.
Devin Booker struggled with four fouls and three field-goals made in the first half, finishing with 17 points, five rebounds and three assists. Paul had four points and four assists in 24 minutes on his return.
The result means the Celtics improved to an NBA-best 21-5 record after three straight wins, while the Suns fall to 16-9.
Giannis powers Bucks to another win
Giannis Antetokounmpo matched Kareem Abdul-Jabbar for the second-longest streak of consecutive 30-point games (eight) in franchise history as the Milwaukee Bucks downed the Sacramento Kings 126-113.
The Greek forward finished with 35 points on 12-of-19 field-goal shooting, with six rebounds and six assists as the Bucks improved to 18-6 with their third straight win. The victory extended the Bucks' win streak against the Kings to 13.
Bucks guard Jrue Holiday made an excellent contribution with 31 points, five rebounds and six assists, while Kings forward Domantas Sabonis added 23 points with 12 rebounds.
Banchero clutch in Magic OT win
Top overall NBA Draft pick Pablo Banchero showcased his potential to help the Orlando Magic snap their nine-game losing streak with a 116-111 overtime win over the Los Angeles Clippers.
The 20-year-old power forward scored 23 points for the game, including making all six of his free-throws in the final seven seconds of overtime to overturn a 111-110 deficit. The Clippers gave up two turnovers down the stretch.
Paul George and Kawhi Leonard made another rare appearance together again, combining for 17 first-quarter points. George finished with 11 for the game with seven rebounds and five assists, while Leonard added 14 points with seven rebounds and three assists.
The Celtics led by as much as 45 points and benched MVP candidate Jayson Tatum in the fourth quarter, in a game where the Suns welcomed back All-Star Chris Paul from a heel injury.
Tatum finished with 25 points with five rebounds, two assists and two steals. The 24-year-old is the first player in Celtics history to average 30 points per game in his first 25 games of any season.
Jaylen Brown also scored 25 points with seven rebounds, while Malcolm Brogdon added 16 points off the bench.
Boston led 69-42 at half-time in the blowout win, which was the Celtics' second-biggest margin this season.
Devin Booker struggled with four fouls and three field-goals made in the first half, finishing with 17 points, five rebounds and three assists. Paul had four points and four assists in 24 minutes on his return.
The result means the Celtics improved to an NBA-best 21-5 record after three straight wins, while the Suns fall to 16-9.
Giannis powers Bucks to another win
Giannis Antetokounmpo matched Kareem Abdul-Jabbar for the second-longest streak of consecutive 30-point games (eight) in franchise history as the Milwaukee Bucks downed the Sacramento Kings 126-113.
The Greek forward finished with 35 points on 12-of-19 field-goal shooting, with six rebounds and six assists as the Bucks improved to 18-6 with their third straight win. The victory extended the Bucks' win streak against the Kings to 13.
Bucks guard Jrue Holiday made an excellent contribution with 31 points, five rebounds and six assists, while Kings forward Domantas Sabonis added 23 points with 12 rebounds.
Banchero clutch in Magic OT win
Top overall NBA Draft pick Pablo Banchero showcased his potential to help the Orlando Magic snap their nine-game losing streak with a 116-111 overtime win over the Los Angeles Clippers.
The 20-year-old power forward scored 23 points for the game, including making all six of his free-throws in the final seven seconds of overtime to overturn a 111-110 deficit. The Clippers gave up two turnovers down the stretch.
Paul George and Kawhi Leonard made another rare appearance together again, combining for 17 first-quarter points. George finished with 11 for the game with seven rebounds and five assists, while Leonard added 14 points with seven rebounds and three assists.
Already up against a 3-1 deficit, it could be curtains for the Celtics' season on Friday when Game 5 comes around.
A regular-season record of 48-24, to Miami's 44-29, had indicated the Celtics should be competitive, while Boston also came out on top in two of their three previous clashes with the Heat in 2019-20.
Yet a 112-109 loss in Game 4 dealt a blow to hopes of reaching the championship series, with 20-year-old rookie Tyler Herro draining a career-high 37 points for Miami who are just a win away now from the NBA Finals.
"It's hard to win a playoff game, right?" head coach Stevens said.
"We're just looking at how can we play better on Friday night. That's the most important game of the season. We need to play our best game yet. That's it."
Coming from 3-1 down to win a best-of-seven series is a daunting challenge, but Stevens is not looking at the prospect of having to win three straight games.
The clear message from the coach is: one game at a time.
"I don't know what the historical odds are," he said. "It doesn't really matter. The situation we're in, we've got to play well Friday. We don't have to win three games on Friday; we have to win one.
"That's going to be our focus. That's going to be our attention. We'll get after it."
Terms of the deal were not disclosed by the Celtics, who hired former Butler University coach Stevens in July 2013.
Stevens has a 318-245 win-loss record since taking charge of the Celtics, with the 43-year-old's wins the fourth-most by any Boston coach in franchise history.
The Celtics will make their sixth successive playoff appearance in 2019-20, while Stevens guided the storied team to back-to-back Eastern Conference Finals between 2017 and 2018.
"Brad is an accomplished coach and an outstanding person," said Celtics lead owner and governor Wyc Grousbeck. "We are proud to have him lead our team forward in our quest for Banner 18."
"We are thrilled that Brad Stevens will continue to be our coach," said Celtics co-owner Steve Pagliuca. "He has become one of the best coaches in the NBA, and is a real leader on and off the court. This is a great day for the Boston Celtics."
The Celtics (48-23) are third in the Eastern Conference this season, behind the high-flying Milwaukee Bucks and defending champions the Toronto Raptors.
Celtics president of basketball operations Danny Ainge added: "Brad is one of the most intelligent and hard-working coaches in the game today.
"More importantly, his character and integrity have contributed to a culture that we all highly value here. Brad is a great team-mate, and a leader people want to follow. We are honoured to have him with us as we continue to pursue our next championship."
Floyd – an African-American man – died in Minneapolis after a police officer was filmed kneeling on his neck during an arrest last week.
Violent protests have broken out across the United States since Floyd's death, during which he was filmed crying out for help as he was handcuffed and pinned to the ground.
"I wrote a letter to our guys this weekend and it took me a while to put down exactly what I wanted to say," Stevens told reporters in a video conference call on Tuesday.
"But I think the thing I wanted them to know, is every decent person is hurting. Every decent person feels the pain of the African-American community. But I also don't want to pretend that I know the exact, distinct pain.
"What I wanted them to know is that I'm with them. I thought that was really important. It's so, so great to see so many of the guys so active... I've talked to a lot of guys. Everybody's hurting. Let's put it that way.
"The leadership they've shown is terrific. And hopefully the most important thing is we can have short-term healing, and we can have near-term gains, and we can have long-term sustainable action that creates change."
Celtics star Jaylen Brown led a peaceful protest in Atlanta last week after driving 15 hours from Boston to his home state of Georgia following Floyd's death.
Brown, who streamed part of the protest live via his Instagram account, marched with a megaphone while holding a sign that said, "I Can't Breathe", a reference to Floyd.
"Jaylen's greatest impact, as good as he is in basketball, won't be in basketball. He's a special guy," Stevens said. "He's a special leader. He's smart, but he has courage. He's got a lot of great stuff to him. I think we recognised that when we drafted him, but he has been even more unbelievable every day, every year.
"I've always personally really enjoyed listening to him and talking to him about things outside of basketball. He told me he was going down there on Thursday and I obviously knew... I'm certainly not surprised by him taking a leadership role. That's who he is."
The Sixers, playing without the injured Ben Simmons, exited the postseason without winning a game in the first round of their Eastern Conference series in Orlando despite 30 points from Joel Embiid and 20 for Tobias Harris in Game 4.
Walker impressed for the Celtics by converting four times from behind the arc, with Jayson Tatum starring to produce 28 points and 15 rebounds, the latter a playoff career high.
The Celtics led by one point at half-time but had extended that advantage to 14 by the end of a dominant third quarter.
Harris was able to return to the game in the fourth quarter after passing concussion tests following a scary fall that saw him land head-first on the court.
But that was the lone positive for the Sixers' as their hopes were emphatically halted at the first hurdle, with their wait for a first NBA Finals appearance since 2001 continuing.
It was the first time in 15 playoff meetings that a series between the two teams had ended in a sweep.
Gallinari was injured playing for Italy in a FIBA World Cup qualifying game against Georgia on Saturday. The Italian national team later announced the veteran sharpshooter sustained a torn meniscus, without providing further details.
ESPN reported on Friday that Gallinari was hopeful of returning late in the 2022-23 season. Typical recovery time for an ACL tear is anywhere from six to 12 months.
The Celtics confirmed on Twitter on Friday: "Danilo Gallinari has been diagnosed with a torn ACL in his left knee. Gallinari sustained the injury while playing for his home nation of Italy in a FIBA World Cup qualifier against Georgia on August 27. Further updates will be provided as appropriate."
Gallinari previously tore the ACL in the same knee while playing for the Denver Nuggets late in the 2012-13 season. That injury required an additional surgery that sidelined him for the entire 2013-14 campaign.
The 34-year-old signed a two-year, $13.3million contract with Boston in July, just days after being waived by San Antonio. Gallinari was acquired by the Spurs from Atlanta on June 30 as part of the trade that sent All-Star point guard Dejounte Murray to the Hawks.
Gallinari, who averaged 11.7 points and 4.7 rebounds in 66 games with the Hawks last season, was being counted on to provide bench scoring for a Celtics team coming off an appearance in the NBA Finals.
He also took to Twitter on Friday to post a statement, saying: "This has been a tough week for me as I have learned the extent of my injury. This game means everything to me and not being able to be on the court with my Celtics teammates hurts.
"I plan to give everything I can to the Celtics organisation and my teammates as we hunt for a title. I will work tirelessly with the Celtics staff to return to the court as soon as I can and I appreciate the unwavering support from the fans, my teammates, and the entire NBA family."
The 13-year veteran is one of only six players to average at least 15 points per game and shoot 40 per cent or better from three-point range over the last four seasons (min. 100 games), along with 2022 All-Stars Stephen Curry and Karl Anthony-Towns, Kyrie Irving, T.J. Warren and Bojan Bogdanovic.
In a stunning year-on-year improvement, the Celtics have been the best defence in the NBA this season after finishing 17th in that department this past season.
With new coach Ime Udoka going all-in on a switching defensive system, it was theoretically going to be tested against the best passing big man in league history, and arguably the league's most dominant offensive force.
However, Jokic was bottled up similarly to everyone else the Celtics have played in 2022, going 8-of-23 (34.7 per cent) from the field in the blowout loss.
Jokic, who is shooting 57 per cent from the field for the season, had previously had his worst shooting performance when he went 6-of-17 (35.3 per cent) in an early-December loss against the Chicago Bulls.
Boston's two superstar wings combined for 60 points, as Jayson Tatum posted 30 points (11-of-17 shooting, 6-of-10 from three) with seven assists, while Jaylen Brown had 30 points (12-of-19 shooting, 3-of-6 from three) with six rebounds.
In a stunning year-on-year improvement, the Celtics have been the best defence in the NBA this season after finishing 17th in that department this past season.
With new coach Ime Udoka going all-in on a switching defensive system, it was theoretically going to be tested against the best passing big man in league history, and arguably the league's most dominant offensive force.
However, Jokic was bottled up similarly to everyone else the Celtics have played in 2022, going 8-of-23 (34.7 per cent) from the field in the blowout loss.
Jokic, who is shooting 57 per cent from the field for the season, had previously had his worst shooting performance when he went 6-of-17 (35.3 per cent) in an early-December loss against the Chicago Bulls.
Boston's two superstar wings combined for 60 points, as Jayson Tatum posted 30 points (11-of-17 shooting, 6-of-10 from three) with seven assists, while Jaylen Brown had 30 points (12-of-19 shooting, 3-of-6 from three) with six rebounds.
The Celtics were too good for the Raptors 122-100 after another even team performance at the Walt Disney World Resort.
Jaylen Brown scored 20 points, with Boston seeing seven players in double-digits for points.
Jayson Tatum (18 points) and Kemba Walker (17) were among them as the Celtics improved to 46-23.
Toronto struggled in defeat, with Fred VanVleet going four-of-14 from the field for his 13 points.
The Brooklyn Nets and Orlando Magic clinched playoff spots in the Eastern Conference.
The Nets were too good for the Sacramento Kings 119-106, while Orlando lost to the Philadelphia 76ers, but secured their spot after the Washington Wizards' loss to the New Orleans Pelicans.
Harris, Embiid lift 76ers as Holiday shines
Tobias Harris (23 points and 15 rebounds) and Joel Embiid (23 points and 13 rebounds) saw the 76ers to their 108-101 win over Orlando.
Jrue Holiday went 11-of-16 from the field for 28 points in the Pelicans' 118-107 victory against the Wizards.
The San Antonio Spurs beat the Utah Jazz 119-111 thanks to 24 points from Derrick White.
Gilgeous-Alexander wayward
Shai Gilgeous-Alexander went three-of-13 from the field as the Oklahoma City Thunder were well beaten by the Memphis Grizzlies 121-92.
Brilliant Brown pass
Brown delivered a wonderful pass to Gordon Hayward in the Celtics' win.
Friday's results
San Antonio Spurs 119-111 Utah Jazz
Memphis Grizzlies 121-92 Oklahoma City Thunder
Brooklyn Nets 119-106 Sacramento Kings
Philadelphia 76ers 108-101 Orlando Magic
New Orleans Pelicans 118-107 Washington Wizards
Boston Celtics 122-100 Toronto Raptors
Lakers face Pacers
The Los Angeles Lakers (51-17) will be aiming to bounce back from back-to-back losses when they face the Indiana Pacers (42-27) on Saturday.
In a rematch of last season's Eastern Conference finals, the Celtics overcame the Heat 107-105 in Miami.
Jayson Tatum (27 points) and Jaylen Brown (21 points and 12 rebounds) led the Celtics (6-3) to their win.
But Payton Pritchard (six points) made the decisive lay-up with 0.2 seconds remaining to secure the win.
The teams kneeled in protest ahead of the clash, in response to a riot on Capitol Hill and after no charges were brought against the police officer who shot and seriously injured Jacob Blake, a black man, in Kenosha in August last year.
Meanwhile, the Bucks made it three straight wins by easing past the Detroit Pistons 130-115.
Giannis Antetokounmpo guided Milwaukee into a 5-3 record with 25 points, eight rebounds and four assists.
Hayward heroic, Beal brilliance not enough for Wizards
Gordon Hayward scored a career-high 44 points to see the Charlotte Hornets past the Atlanta Hawks 102-94.
Bradley Beal equalled a Washington Wizards record, but it was not enough. Beal tied the franchise record with 60 points in a 141-136 loss to the Philadelphia 76ers.
Joel Embiid once again inspired the 76ers, scoring 38 points to go with eight rebounds and five assists as they improved to 7-1.
A 35-point haul from Malcolm Brogdon helped the Indiana Pacers beat the Houston Rockets 114-107.
Curry cools off
After 92 points in the previous two games, Stephen Curry cooled off. He went five-of-17 from the field for 13 points in 35 minutes as the Golden State Warriors fell to the Los Angeles Clippers 108-101.
Beal ties record
Beal was in spectacular form for the Wizards. He equalled Gilbert Arenas' record of 60 points for the Wizards against the Los Angeles Lakers in 2006.
Wednesday's results
Indiana Pacers 114-107 Houston Rockets
Orlando Magic 105-94 Cleveland Cavaliers
Philadelphia 76ers 141-136 Washington Wizards
Charlotte Hornets 102-94 Atlanta Hawks
Boston Celtics 107-105 Miami Heat
New York Knicks 112-100 Utah Jazz
Milwaukee Bucks 130-115 Detroit Pistons
Oklahoma City Thunder 111-110 New Orleans Pelicans
Phoenix Suns 123-115 Toronto Raptors
Los Angeles Clippers 108-101 Golden State Warriors
Sacramento Kings 128-124 Chicago Bulls
76ers at Nets
The 76ers will look to continue their good start to the season when they take on the Brooklyn Nets (4-4). The Nets will again be without star Kevin Durant, who is in quarantine.
Jayson Tatum notched up 39 points on 13-of-29 shooting, six assists, five rebounds and six steals in the win for the Celtics, who continued to lock down Kevin Durant.
Though Durant shot 54.5 per cent from the floor, moving him to 17-of-52 for the series, he did it on 11 shots on Saturday as the flexible and intense Celtics defensive scheme continued to force the ball out of his hands. Kyrie Irving also went six-of-17 from the floor.
Bruce Brown was the highest scorer for the Nets with 26 points on 10-of-19 shooting, but he and Durant contributed to 10 of the team's 20 turnovers, from which Boston scored 25 points.
The Celtics led for the whole of the second half and whenever the Nets would threaten with a scoring run, managed to make timely buckets and secure a big road win.
Gobert gets up for Jazz win
Luka Doncic's return from injury was not enough for the Dallas Mavericks as the Utah Jazz evened up their series at 2-2, earning a 100-99 win.
Rudy Gobert gave Utah the lead with an alley-oop dunk with 11 seconds remaining in Game 4, before Spencer Dinwiddie missed a three-ball at the buzzer for the Mavs.
While Doncic had 30 points in his first game back from a strained calf, Dallas were kept to just 18 points in the fourth quarter, shooting six-of-18 from the floor.
Siakam sizzles as Raptors avoid sweep
Pascal Siakam scored 15 of his of 34 points in the fourth quarter as the Toronto Raptors avoided a series sweep, defeating the Philadelphia 76ers 110-102.
Despite a 19-point deficit in points off turnovers, Toronto continually managed to penetrate and get on the break, holding a combined 25-point advantage for points in the paint and fast-break points.
Nursing an injured thumb, Joel Embiid shot seven-of-16 from the floor for his 21 points to go with eight rebounds, but also coughed up five turnovers.
Timberwolves level series with Grizzlies
Karl-Anthony Towns bounced back from a disappointing Game 3 to help the Minnesota Timberwolves even their playoff series with the Memphis Grizzlies, winning 119-118.
After going missing in Game 3, taking only four shots as the Grizzlies overcame a 26-point deficit, Towns was more assertive from the outset, adding 13 rebounds to 33 points.
Anthony Edwards' fingerprints were all over the game however, coming up with 24 points on seven-of-14 shooting, four rebounds, four assists, two steals and three blocks.
With the Eastern Conference semi-final playoff series deadlocked at 3-3, it was a winner-takes-all clash in Orlando, Florida on Friday.
Boston emerged triumphant against the second-seeded Raptors 4-3 to earn a showdown with the Miami Heat thanks to Jayson Tatum's double-double of 29 points and 12 rebounds.
The Denver Nuggets, meanwhile, stayed alive after topping the Los Angeles Clippers 111-105 in Game 5 of their Western Conference semi-final.
Denver were facing elimination but the Nuggets overturned a 15-point deficit to reduce the Clippers' lead to 3-2 at Walt Disney World Resort.
Jokic and Murray lift Nuggets
Denver's star duo produced when it mattered most. Nikola Jokic put up 22 points and 14 rebounds, while Jamal Murray had 26 points for the rallying Nuggets.
Kawhi Leonard posted a game-high 36 points and nine rebounds but it was not enough for second seeds the Clippers, while team-mate Paul George finished with 26 points.
Jaylen Brown recorded 21 points as the Celtics reached the Conference finals for the third time in four years.
Celtics struggled from free-throw line
While the Celtics progressed, they shot just 56.5 per cent from the free-throw line, making only 13 of their 23 attempts.
Lou Williams was far from his best for the Clippers. He was two of 10 from the field, while missing all five of his three-pointers. Williams ended the game with four points in 19 minutes.
Rockets face Lakers
Western Conference top seeds the Los Angeles Lakers can book their passage through to the next round if they beat the Houston Rockets on Saturday. LeBron James and the Lakers lead 3-1.
The 12-time All-Star forward rocked the Brooklyn Nets by requesting a trade last month, having joined the franchise in 2019.
Having won back-to-back NBA titles in 2017 and 2018 during his time with the Golden State Warriors, being named the finals' MVP on both occasions, Durant has reportedly shown signs of discontent with the Nets' failure to compete for a first-ever NBA title.
The Nets' 2022 playoff campaign was halted by a first-round defeat to the Celtics, who now appear to be in the hunt for Durant's signature.
According to a report from ESPN's Adrian Wojnarowski, the Celtics' ability to include 2021 All-star forward Jaylen Brown in any deal makes them a strong contender to acquire Durant, who is under contract until 2026.
Durant is expected to command a huge trade package, and ESPN claim Boston could offer as many as three unprotected first-round picks and two pick swaps alongside Brown's services.
The Miami Heat, the Phoenix Suns and the Toronto Raptors have also been credited with an interest in Durant, who led the Nets with an average of 29.9 points per game across his 2021-22 regular-season campaign, posting a 36-19 record in his 55 outings.
Brown only shot four-of-13 for 12 points in the Celtics' Game 1 defeat, but followed up by scoring 30 points, with six assists and five rebounds as Boston levelled the series at 1-1 at TD Garden.
The 25-year-old also sank a playoff career-high six shots from beyond the arc and stated after the victory just how much the Celtics had wanted to square things up.
"We knew we had to come out and play like our season was on the line and we did that," Brown said.
"It's the playoffs. Survival of the fittest. Every game counts."
As well as Brown's performance, Jayson Tatum also stepped it up as he shot 29 points, with eight assists and three rebounds.
Boston coach Ime Udoka pointed to what his team had learned in their Game 1 defeat, namely not to get "outmuscled", and just as they were dominated for large periods on Sunday, they followed up with a physical performance of their own on Tuesday.
"We adjusted well," Udoka said. "We learned some things from Game 1 and felt like we knew we didn't react accordingly to the way that we're playing.
"Two big teams but we haven't been outmuscled like that all year. I think our guys took pride in that, took that to heart and we knew we would come out with the right effort tonight."
His opposite number, Bucks coach Mike Budenholzer, acknowledged the game-plan from the Celtics had worked, particularly on star player Giannis Antetokounmpo, who still finished with 28 points, with nine rebounds and seven assists.
"The guys on him, they're solid, good, good defenders and then quite a bit of help," Budenholzer said. "That's where he's just got to see and feel it. Do we kick it and get more threes? Or he's got to finish against one-on-one defense. So, I think it's a little bit of both.
"But Giannis, he always figures things out."
Hayward had 12 points as the Celtics triumphed 109-101 in Game 1 of their first-round series in the NBA playoffs.
He twisted his right ankle - fortunately not the same one he suffered a gruesome injury on back in 2017 - as he tried to box out Sixers center Joel Embiid with just over three minutes to go in the fourth quarter.
As a result, Hayward will undergo a scan to ascertain the severity of the problem.
"Sprained ankle," Celtics coach Brad Stevens said. "Don't know the severity, but he's clearly in pain.
"It looked like it had some swelling already. That is my medical review."
Marcus Smart would be expected to replace Hayward in the starting line-up if he has to miss any time.
Jayson Tatum had 32 points and 13 rebounds – both career playoff highs - for the victorious Celtics, with Jaylen Brown adding 29 in the NBA bubble at the Walt Disney World Resort in Orlando.
"We came out and we battled," said Brown, whose team overcame a Sixers side playing without the injured Ben Simmons.
"We were the more physical team and we came out on top. I was proud of us. We've got to keep that fight up if we want to win this series.
"Who wants it the most? Who wants to fight? That is what it comes down to.
"Experience is everything. That's the best teacher. I've been lucky enough to go to two Eastern Conference finals, so I feel like I bring a lot of experience.
"[Tatum] also has been to a conference finals, so continue to feed that to our young guys and play like you've been here before."
Game 2 will take place on Wednesday.
Williams made physical contact with referee Cheryl Flores, after he jumped up in anger after being called for an offensive blocking foul while defending Zach LaVine in the fourth quarter.
The Celtics forward was immediately given a technical foul and ejected from the game.
Williams had to be restrained by teammate Derrick White, before being escorted off the court as he yelled back towards the court as he headed towards the locker room.
NBA executive vice president, head of basketball operations Joe Dumars announced the suspension for "recklessly making contact with and directing inappropriate language toward a game official" on Wednesday.
Williams will serve the one-game suspension in Friday's game against the Cleveland Cavaliers.
Darius Garland is in contention to return for the Cavs in that game, having been out since suffering a left eye injury in their season opener against the Toronto Raptors.
The Cavs' All-Star participated in team shootaround on Wednesday while wearing goggles for protection but missed the 103-92 win over the Orlando Magic later that day.
Holiday made good on 11 of 14 field goal attempts to help offset a rare off-shooting night from Jayson Tatum and help the Eastern Conference champion Celtics move within two wins of their first NBA title since 2008.
Tatum struggled to a 6-of-22 performance from the field, though the All-Star forward did contribute 12 assists and nine rebounds as Boston withstood a triple-double from Dallas' Luka Dončić and earned its ninth straight win of this post-season.
Doncic compiled 32 points, 11 rebounds and 11 assists in 42 minutes despite being a game-time decision. The NBA MVP finalist was listed as questionable for Game 2 due to a chest contusion he presumably sustained during Dallas' 107-89 loss in Thursday's series opener.
He added four steals but committed eight of the Mavericks' 15 turnovers on the night, while backcourt mate Kyrie Irving was held to 7-of-18 shooting while managing 16 points.
The Western Conference champions will attempt to avoid an 0-3 hole when they return home to host Wednesday's Game 3, though the Celtics are 6-0 on the road in these play-offs.
Dallas couldn't overcome a 21-point half-time deficit in Game 1, but it led 55-54 early in the second half of this one before the Celtics began to assert control late in the third quarter.
Boston used a 10-0 run, capped by Holiday's layup off a Tatum feed, to build a 75-63 advantage with under three minutes left in the period. The Celtics never trailed thereafter, though Dallas made a bid to get back in it late.
Down 14 with under 3 1/2 minutes remaining, the Mavericks scored nine straight points to pull within 103-98 on Doncic's 3-point play with 1:15 to go.
Dallas had a chance to move closer, but PJ Washington's dunk attempt in the final minute was blocked by Derrick White. Jaylen Brown then drove the lane and scored on the ensuing possession to extend Boston's margin to seven points with less than 30 seconds left.
Brown finished with 21 points and seven assists, while White had 18 points and went 4 of 10 from 3-point range.
Holiday recorded 17 first-half points on 7-of-9 shooting, though the Celtics took a slim 54-51 lead into the break as Doncic kept Dallas close with 23 points on a 9-of-13 success rate.
