Boston’s Al Horford shows some emotion after dunking over Milwaukee’s Giannis Antetokounmpo during the second half of Game 4 on Monday in Milwaukee. The Celtics won 116-108 to tie the series 2-2. Morry Gash/Associated Press

MILWAUKEE — If the Celtics go on to win their Eastern Conference semifinal series against the defending champion Milwaukee Bucks, the image of Al Horford nodding at Giannis Antetokounmpo’s trash talk could become a cult favorite highlight.

The moment came with 10:56 left in the third quarter of Game 4 on Monday night. Antetokounmpo was starting to take over the game, and after a dunk on Horford, he had some trash talk for the Celtics’ big man. Antetokounmpo eventually picked up the technical foul because of his antics, and Horford couldn’t hear him, but the message was received.

And Horford didn’t like it.

“The way that he was looking at me and the way he was going about it really didn’t sit well with me,” Horford said. “And I think at that point, something switched with me in the game.”

All Horford did the rest of the game was put up some of the best numbers of his long career. Horford scored a playoff career-high 30 points on 11-for-14 shooting when the Celtics desperately needed a boost. Boston endured a frustrating third quarter, was only down seven points heading into the fourth.

Horford also put Antetokounmpo on a poster with an impressive dunk early in the fourth quarter. He picked up his own tech on the dunk, but he sent the two-time MVP on the opposite end of the highlight reel. And he did it all at 35 years old as the Celtics beat the Bucks 116-108.

“I didn’t see the follow through on what he did, but it sounded like he cracked him pretty good, energized the group,” Boston Coach Ime Udoka said of Horford’s dunk. “He’s been great all year, but we really needed him to step up with guys being out. He took that on his shoulders. They guard him a certain way, he’s able to attack. Love the aggressiveness.”

The fourth quarter was when Horford turned it on. He hit 3s, he defended and he finished 6 for 6 from the field for 16 points in the fourth alone. Sprinkle in some Jayson Tatum heroics – 12 of his 30 points were in the fourth quarter – and the Celtics completed the comeback victory.

But the dunk appeared to be the start of it all. Horford tied the score at 80-80 on the momentum-altering play, and the Celtics said they were juiced up by their veteran’s heroics.

That’s exactly what the Celtics needed to tie the second-round series at 2-2. It’s now a best-of-three series, and the Celtics snatched back the all-important home-court advantage. If Horford continues to play like he’s 25, not 35, the Celtics look even more dangerous.

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

LOST IN HORFORD’S incredible game was a bounce-back game by Jayson Tatum. The star’s 30 points weren’t as efficient as Horford, but he looked more aggressive and assertive Monday compared to his Game 3 dud. Tatum had just 10 points and three assists in the Celtics’ 103-101 loss on Saturday.

Getting Tatum going is important for the Celtics as no one else on the team can carry them like he can. Tatum was 11 for 24 from the field, and added 13 rebounds and five assists on Monday. It was far from a perfect effort, but he was important when the team needed him. He scored 12 points in the fourth quarter, doing most of his damage after Horford’s scoring explosion.

“I played terrible Game 3 and we almost had a chance to win, and that was really the toughest part, just knowing that,” Tatum said. “So I was just really eager to get back and ready to play and whether it was scoring or not, just coming out and just playing better on both ends of the floor, and doing what I can to help us get a win.

ASIDE FROM HORFORD, it was a forgettable night for both Grant Williams and Daniel Theis. While Theis hasn’t played many minutes this series, he was forced into action because Robert Williams was unavailable for Game 4 with knee soreness. Theis struggled in his 11 minutes of action, going 0 for 5 from the field.

Grant Williams got the starting nod, but he was haphazards in his 25 minutes. Williams has provided some valuable minutes for the Celtics, but it wasn’t his night Monday.