BOSTON — Of all the predictions for how Game 7 of the Eastern Conference semifinals might play out, Grant Williams leading the Boston Celtics in scoring against the defending NBA champions was not high on anyone's list.

Dared to shoot by the Milwaukee Bucks, Williams made seven of Boston's 22 3-pointers in a resounding 109-81 victory to eliminate two-time MVP Giannis Antetokounmpo and the league's 2021 champions.

Jayson Tatum finished with 23 points, eight assists and six rebounds for the Celtics. Jaylen Brown added 19 points, but it was Boston's role players who turned a close first half into a rout. Williams (game-high 27 points), Payton Pritchard (12 points) and Marcus Smart (11 points, 10 assists, seven rebounds) were immense.

Antetokounmpo amassed 25 points, 20 rebounds and nine assists, but he required 26 shots to get there.

The Celtics withstood Antetokounmpo's early onslaught, which had him approaching a triple-double in the opening 12 minutes, and their own miserable shooting (7-24 FG) to exit the first quarter only down 26-20.

A Pritchard pass to Al Horford capped a 12-4 run and gave Boston a 32-30 lead in the opening four minutes of the second quarter. The Bucks responded with seven straight points, highlighted by the interior presence of Brook Lopez on both ends. The lead changed seven times in the quarter, until Williams — consistently left open by Milwaukee's defense — found the net with a 3-pointer inside the final minute.

In a wild finish to the half, Marcus Smart pilfered Antetokounmpo, who fouled the Celtics guard on a halfcourt heave attempt with 0.9 seconds left. The three free throws gave Boston a 48-43 halftime lead.

Williams, Tatum and Brown all made 3-pointers in the first two minutes of the third quarter, stretching Boston's lead to 59-47 and forcing a Milwaukee timeout. Not even Tatum's fourth foul — on a controversial charge call that negated a three-point play — could stop the Celtics from rolling into the fourth quarter. Brown and Williams combined for 20 points in the third, extending the lead to 79-64 without their superstar.

The advantage grew to 28 points by the final buzzer, as the Bucks played uncharacteristically out of sync offensively and opted to leave Boston's red-hot role players wide open for knockdown 3-point attempts. The Celtics outscored the Bucks 66-12 from the 3-point line. Milwaukee shot 37% from the field and 12% (4-33) from beyond the arc, which was hardly enough to extend its title defense beyond the second round.

The Celtics visit the Miami Heat for Game 1 of the Eastern Conference finals on Tuesday at 8:30 p.m. ET.

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Ben Rohrbach is a staff writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach