BOSTON — The Chicago Bulls waited until the final night of the regular season to cement their spot in the postseason. Jimmy Butler made sure the wait for a playoff victory was a short one.

Butler had 30 points and nine rebounds and the Bulls outlasted top-seeded Boston 106-102 in Game 1 on Sunday on an emotional night for grieving Celtics star Isaiah Thomas.

Playing a day after 22-year-old sister Chyna Thomas was killed in a car accident in their home state of Washington, Thomas led the Celtics with 33 points. But Butler overcame a united Garden crowd and led Chicago to the victory, scoring 23 points in the second half.

“We were so locked in all week,” Butler said. “We knew their stuff, just like they knew ours. But we executed extremely well. We haven’t done that all season, but this is the right time to do it.”

He also got a big lift from the Bulls’ young reserves, who outscored their Boston counterparts 35-22.

Bobby Portis finished with 19 for the Bulls.

Chicago Coach Fred Hoiberg lauded his team’s defensive effort, particularly how it outrebounded Boston 53-36. He also had praise for the job Butler did defending Thomas late, after Rajon Rondo picked up his fifth foul.

“Jimmy is obviously our best defender,” he said. “Jimmy is going to have his turn to guard him.”

Rondo said they wanted to be aggressive.

“I told the guys coming out it was going to be physical and we wanted to throw the first punch,” he said.

Al Horford had 19 points, eight assists and seven rebounds for the Celtics. He was active throughout, coming up with several big baskets and assists to keep his team in the game.

Game 2 in the first-round series is Tuesday night in Boston.

Neither team had more than a two-possession lead until Butler made three free throws with 4 minutes to play to make it 95-88. Butler scored 10 straight points to put the Bulls back in front early in the fourth, the first of three lead changes in the fourth.

Later, Thomas had a scary moment when he was hit on his left hand on a 3-point attempt before landing awkwardly on it. After a quick visit to the trainer, he calmly made all three free throws.

It was part of a stretch in which he scored seven straight points.

Celtics fans rallied behind Thomas, showering him with a deafening cheer when he was introduced.

Still, Thomas appeared to be a little emotional at the start of the game, badly missing his first free throw short off the front rim. He wasn’t the only Boston player a little off their game in the first half. Boston’s second unit started the second quarter 1 for 7 from the field and was outscored 10-0 to surrender the Celtics’ first-quarter lead.

The Bulls also had their moments of fallibility.

Late in the second quarter Wade intercepted an errant pass by Thomas, but got hung on the front of the rim as he attempted a dunk on the fast break.

Horford he acknowledged afterward that emotions were tough for not just Thomas, but the entire team.

NOTES: Thomas recorded his second career 30-point game in the postseason. He had 42 against the Hawks last season. … Horford has now scored in double figures in each of his last six postseason games. … Boston was 18 for 45 from the field in the first half.