Milwaukee’s Giannis Antetokounmpo, right, and Boston’s Jaylen Brown battle during the first half Monday in Milwaukee. Morry Gash/Associated Press

MILWAUKEE — Al Horford has played in more than two dozen postseason series in a 15-year NBA career but rarely has outwardly shown much emotion during all those appearances.

That all changed Monday night.

The 35-year-old Horford had just capped a 10-0 run by driving down the baseline, hitting a game-tying dunk and drawing a foul on two-time MVP Giannis Antetokounmpo. Horford celebrated by letting out a scream and pumping his fists.

Horford’s big moment was the signature play in a fourth-quarter comeback that enabled the Boston Celtics to beat the Milwaukee Bucks 116-108 and tie their Eastern Conference semifinal at two games apiece.

“I usually just kind of go about my business,” said Horford, who finished with a career playoff-high 30 points. “I do get excited, but I guess you kind of pick your spots, your moments. This was an emotional game.”

The teams have alternated victories in this best-of-seven series, which continues Wednesday with Game 5 in Boston.

Boston tied the series mainly because of Horford and Jayson Tatum, who also had 30 points. Horford had 16 points and Tatum 12 in the fourth quarter alone to help the Celtics outscore the defending NBA champions 43-28.

“We love Al,” said Boston’s Marcus Smart, who scored 18 points. “Best vet we’ve ever had. Best vet I’ve ever had. He comes in, never changes whether things are going bad or good. He’s going to be him, and nine times out of 10, it’s going to work out in our favor.”

Horford and Tatum helped the Celtics rally even while Jaylen Brown dealt with foul trouble that caused him to play less than half of the fourth quarter. The Celtics played the whole game without forward/center Robert Williams, who was out with soreness in his surgically repaired left knee.

Horford had Boston’s first six points and Tatum the last eight during a 14-2 run that put the Celtics ahead for good and gave them a 106-96 advantage with 3:33 left. The Bucks wouldn’t cut the margin below six the rest of the way.

Tatum had 13 rebounds and five assists while bouncing back from a poor performance in a 103-101 Game 3 loss, when he had 10 points and shot 4 for 19.

“I played a terrible Game 3 and we almost had a chance to win,” Tatum said. “That was really the toughest part, was knowing that. I was really eager to get back and ready to play.”

Horford said he was motivated by an encounter he had earlier in the game with Antetokounmpo, who had 34 points, 18 rebounds and five assists.

Antetokounmpo drew a technical foul in the first half when he stared down Horford after a dunk.

“I don’t really know what he said to me, but the way he was looking at me and the way he was going about it, really didn’t sit well with me,” Horford said. “At that point, I think just something switched with me in the game.”

Horford got his own technical foul on his game-tying dunk because his left arm landed on Antetokounmpo’s face as he was coming down.

After shooting just 40% through the first three quarters of the game, the Celtics went 16 of 19 overall and 4 of 5 from 3-point range in the final period. Horford was 6 of 6 and Tatum 5 of 6.

“Down the stretch, they made shots,” Antetokounmpo said. “They executed well. They were disciplined.”

Horford sparked the rally after Boston trailed by 11 late in the third quarter.

The Celtics tied the game on Horford’s dunk with 9:51 left in the game, but that was just one of several huge plays he made.

After Brook Lopez scored the game’s next four points to put the Bucks back ahead, the Celtics responded with a 7-0 run and broke an 85-all tie on Horford’s 3-pointer with 8:08 left.

The Bucks regained the lead 94-92 when Antetokounmpo hit a driving layup and drew a foul on Horford with 6:02 left. But after Antetokounmpo missed the free throw, Horford started the 14-2 run that put the Celtics in control.

“Al had a hell of a game,” said Milwaukee’s Jrue Holiday, who scored 16 points but shot 5 of 22. ” I think we came down and had some shots we usually make, and we couldn’t finish those. But give them credit. They made more plays.”

Horford hit a corner 3-pointer to put the Celtics back ahead with 5:40 left and followed that with a conventional three-point play that made it 98-94 with 5:09 remaining.

After the Celtics lost Game 3 because his potential tying basket came just after the buzzer, Horford made sure this series returned to Boston all tied up.

“We all understood the importance of this game,” Horford said. “We felt at the end of Game 3 we were in position to win the game, and we didn’t. I was just really locked in. I understood the moment, what we needed to do as a group. I really just did whatever it took tonight. It was one of those type of nights.”

NOTES: The Bucks played a seventh straight game without three-time All-Star forward Khris Middleton due to a sprained medial collateral ligament in his left knee. As for the Celtics, Coach Ime Udoka expressed optimism before Monday’s game that Williams would be available for Game 5 … Grant Williams replaced Robert Williams in the lineup and made his first career playoff start. … Horford’s previous career playoff high was 26. He had reached that total three times. He also was 5 of 7 on 3-point attempts and had his highest career playoff total for 3-point baskets.