Celtics top Bucks in overtime.

BOSTON (AP) — Boston coach Brad Stevens loves the postseason because it offers a chance to "bust narratives."

The Celtics took their first step toward shattering the belief they can't win without their biggest stars.

Al Horford had 24 points and 12 rebounds and Boston overcame Khris Middleton's long 3 that beat the fourth-quarter buzzer, topping the Milwaukee Bucks 113-107 in overtime Sunday to open the playoffs.

The Celtics led 99-96 with 0.5 seconds left in regulation when Middleton took an inbounds pass on the far right wing and hit a contested 35-footer. Boston outscored Milwaukee 14-8 in the extra period.

Terry Rozier added 23 points, four rebounds and three assists for Boston in his first career playoff start. Jaylen Brown finished with 20 points. Rookie Jayson Tatum added 19 points and 10 rebounds.

Rozier said he knows he's under a spotlight this postseason with Kyrie Irving out for the season following his recent knee surgery.

"I just know I gotta step up," he said. "I know I gotta fill big shoes. I don't feel no pressure. I'm glad to be in this position."

Game 2 in the best-of-seven series is Tuesday night in Boston.

Giannis Antetokounmpo led the Bucks with 35 points, 13 rebounds and seven assists before fouling out in overtime. Middleton had 31 points, eight rebounds and six assists. Malcolm Brogdon scored all 16 of his points after halftime.

After a muted start, things opened for Antetokounmpo. But he said he must do a better job the defensive end against Horford going forward.

"He knows what he's doing down there," Antetokounmpo said. "Hopefully in Game 2 I won't play on my heels and I'll play more on my toes and be able to defend without fouling."

Part of the reason the Bucks were in bad spots is because they were hampered by turnovers. They committed 20, leading to 27 Boston points.

"That's not getting shot up," Middleton said. "We feel like if we get a shot up, we'll be good."

An acrobatic, spinning layup by Tatum gave Boston a 108-105 lead in overtime.

It was 108-106 when Horford snared a rebound and got it ahead to Rozier, who was fouled. He made two free throws to put the Celtics in front 110-106 with 18.8 remaining.

Antetokounmpo made one of two foul shots with 14.8 seconds left, but he fouled out of the game while going for the rebound on his miss.

Rozier added three free throws to provide the final margin.