Al Horford's career-best playoff haul of 30 points drew acclaim as the Boston Celtics secured Game 4 with a superb fourth quarter in a 116-108 road win over the Milwaukee Bucks.

The 35-year-old veteran and five-time NBA All-Star delivered 11-of-14 shooting with eight rebounds and three assists as Boston levelled the NBA Eastern Conference semi-final series at 2-2.

Horford rose to the occasion after a third-quarter dunk from Giannis Antetokounmpo left him smarting, and steered the visitors to a crucial win at the Fiserv Forum in Wisconsin.

The center returned the favour on his opponent in the final act, with both handed technical fouls, but it was the sheer energy of the Dominican that captured the attention.

"That was a hell of a play," team-mate Jayson Tatum said. "Especially anytime Al turns back the clock and he looks like his old self, it gets everybody off the bench.

"Al plays with so much passion. When Al is playing with passion like that, everybody else has to follow."

Marcus Smart also hailed Horford, in particular for his dunk, adding: "It's a big-time play in a big-time moment.

"It's a physical game. We were on the other end a couple of times, so it felt kind of good to have that one."

Horford himself admitted the Celtics were driven to victory by a desire to close out the game after the Bucks held on for a 103-101 win on Saturday in Game 3.

"We felt that at the end of Game 3 that we were in a position to win the game, and we didn't," he added. "I was just really locked in.

"I understood the moment and what we needed to do as a group. Just come out and we were gonna do whatever it took tonight. It was one of those types of nights."

The two sides return to Massachusetts now, and will contest Game 5 at the TD Garden on Wednesday.

The Boston Celtics produced an incredible fourth quarter to take Game 4 116-108 on the road against the Milwaukee Bucks, tying the NBA Eastern Conference semi-final series at 2-2.

A strong start for home side Milwaukee saw them hold the Celtics to just 18 points in the first quarter, but the tough play of Al Horford, Derrick White and Jaylen Brown helped the visitors back into the game, trailing 48-47 at half-time.

Performances went up a gear in the second half, as a massive Giannis Antetokounmpo dunk on Horford was then reciprocated, with both players receiving technical fouls after their respective dunks.

After a quiet start, Jayson Tatum began to find his footing, eventually taking over to score 20 of his 30 points in the second half, going 11-of-24 from the field overall with 13 rebounds and five assists.

Tatum was vital to the Celtics, but Horford was their best player, with 30 points on 11-of-14 shooting with eight rebounds and three assists, while also being their primary source of interior defence.

There were times when it appeared Antetokounmpo simply would not be denied, going on to post game-highs in points with 34 (14-of-32 shooting) and rebounds with 18, but he needed far more offensive help from Jrue Holiday, who shot just five-of-22 from the field for his 16 points to go with his nine assists and seven rebounds.

Antetokounmpo's 13 points in the third quarter guided the Bucks to a 80-73 lead at three-quarter time, but there would be nothing they could do about the offensive onslaught that was to come.

In the final frame, the Celtics shot 16-of-19 from the field (84 per cent), four-of-five from three-point range and seven-of-seven from the free-throw line, winning the quarter 43-28 and pulling away down the stretch.

Game 5 will head back to Boston, with Game 6 scheduled to return to Milwaukee. Game 7, if needed, will be played in Boston.

Chef Curry cooks up late comeback

The Memphis Grizzlies lacked the firepower to match the Golden State Warriors down the stretch, going down 101-98 as the Warriors established a 3-1 series lead in their Western Conference semi-final.

Without Ja Morant, who missed the game after suffering a knee injury in Game 3, the Grizzlies fought gallantly, leading at quarter-time, half-time and three-quarter time as their defense rose to the occasion and turned it into a scrap.

With Jaren Jackson Jr dominating around the rim – blocking five shots and snatching two steals – the Warriors were held to just 38 points in the first half, but poor shooting from Jackson (seven-of-21) and Dillon Brooks (five-of-19) bogged down the Grizzlies offense.

Needing a hero in the fourth quarter, Warriors superstar Stephen Curry stepped up, scoring 18 of his 32 points, including eight consecutive clutch free throws in the final minute, as his team edged ahead and clung on to a narrow lead.

Curry shot 10-of-25 from the field across the game, and four-of-14 from long range, with eight assists and five rebounds.

Andrew Wiggins was arguably the Warriors' strongest performer across all four quarters, shooting seven-of-13 for his 17 points, with five of his 10 rebounds coming on the offensive end, and he added two blocks and one steal to finish with a team-high plus/minus of plus 12.

Otto Porter – who is still just 28 years old and set to become an unrestricted free agent – continues to make himself money this postseason as he played a crucial 26 minutes off the bench, shooting four-of-six from long range and adding three assists with two steals.

Memphis Grizzlies superstar Ja Morant has officially been ruled out of Game 4 against the Golden State Warriors due to a knee injury he suffered in Game 3.

Morant, who was the winner of this season's Most Improved Player award, has averaged 38.3 points, 8.3 assists and 6.7 rebounds per game through the first three fixtures of the series.

It appeared Morant had a knee-on-knee clash in Game 3, but the Grizzlies highlighted a sequence where Morant got tangled up with Jordan Poole during a double-team near half-court, where Poole appeared to grab Morant's knee and pull it.

While it seemed innocuous, with the NBA announcing Poole would face no repercussions, Morant tweeted a video of the incident immediately after the game with the caption "broke the code" – before deleting the tweet.

The "code" Morant is referencing touches on a comment made by Warriors coach Steve Kerr, when he said Grizzlies guard Dillon Brooks "broke the code" with his flagrant two foul on Gary Payton II that caused a fractured elbow and sidelined the defensive specialist through at least the rest of the series.

While Morant's absence will be clearly felt, the Grizzlies may be the team most equipped to survive for a game without their star, finishing the regular season with a 20-5 record in the 25 games Morant missed.

Game 4 will be played at the home of Golden State, before returning to Memphis for Game 5. 

Golden State Warriors head coach Steve Kerr has tested positive for COVID-19 and will miss Game 4 against the Memphis Grizzlies.

Assistant coach Mike Brown will step in as acting head coach – a role he is familiar with.

During the Warriors' 2017 championship run, Brown went 12-0 as acting head coach in the playoffs as Kerr was sidelined for an extended period, with the Warriors ultimately finishing that postseason with a 16-1 record.

It is interesting timing for Brown, who was announced as the next Sacramento Kings head coach on Sunday.

He has been with the Warriors since 2016, after spending 10 years as a successful head coach beforehand, winning over 61 per cent of his games with the Cleveland Cavaliers and Los Angeles Lakers.