Grant Williams scored a career-high 27 points as the Boston Celtics advanced to the Eastern Conference finals, defeating the reigning NBA champion Milwaukee Bucks 109-81 in Game 7 on Sunday.

Williams went seven-of-18 from the perimeter to lead the Celtics, with four others scoring in double digits in Jayson Tatum, Marcus Smart, Jaylen Brown and Payton Pritchard, who added 14 points off the bench.

The 23-year-old's seventh triple of the night came at an important time, too, with the Bucks starting to gather momentum at the beginning of the fourth quarter.

Tatum was pivotal on both ends despite seven turnovers, putting up 23 points on 50 per cent shooting, eight assists and six rebounds.

The Celtics were able to restrict Giannis Antetokounmpo from scoring easily, with the reigning finals MVP getting 25 points but on 10-of-26 shooting, along with his 20 rebounds and nine assists.

With the series-deciding win, the Celtics have set up a rematch of the 2020 Eastern Conference finals, facing the first-seeded Miami Heat.

Doncic dominates as Mavs demolish Suns

Both of the contestants in the 2021 NBA finals were knocked out in same night in Game 7s on Sunday, with the Dallas Mavericks blowing out the first-seeded Phoenix Suns 123-84.

The Suns scored a disappointingly low 27 points on their home floor in the first half, as threes rained in on the other end, and the Mavs went into the main change with a 30-point lead.

Chris Paul and Devin Booker went missing when they were needed most, generating little in terms of dribble penetration and combining for 21 points on seven-of-22 shooting.

Conversely, Luka Doncic had come into Game 7 with shooting splits of 45.7 and 29.6 per cent but lit the Suns up with the season on the line, finishing with 35 points on 12-of-19 shooting.

More importantly, Doncic was able to get his teammates good looks, with Dallas shooting an 48.7 per cent from the perimeter.

The Mavericks will now face the Golden State Warriors in the Western Conference finals.