Tatum seemed to find his groove at the end and helped finish off the Bucks with his 30-point night. Giannis Antetokounmpo had 34 points and 18 rebounds for Milwaukee.
The Celtics regained home-court advantage and now know the route to the conference finals will once again go through TD Garden. Game 5 will be played in Boston on Wednesday night.
The Celtics trailed, 80-73, at the start of the fourth, with Brown on the bench with five fouls. But Horford would not let them fade. He erupted for 10 points over the first four minutes of the quarter, including a violent one-handed slam as he was fouled by Antetokounmpo, and a 3-pointer with 8:08 left that gave Boston an 88-85 lead, tied for its largest to that point.
After the Bucks pushed back in front, 94-92, on an Antetokounmpo layup, Horford answered with a 3-pointer and a 3-point play, giving the Celtics a 98-94 advantage.
Then Tatum put together one of the dominant stretches that became so familiar during his All-NBA caliber season, pouring in 10 points over a 98-second stretch to put the Bucks away.
Observations from the game:
▪ Tatum, who was coming off perhaps the worst playoff game of his career, started the game by badly missing a 3-pointer badly but he attacked for a strong one-handed dunk over Brook Lopez. It was the kind of play that can get a struggling player going. He rolled in a mid-range jumper a few minutes later, but picked up his second foul when he pushed off while clearing space near the foul line in the final minute of the first quarter. Those push-offs have become too common for Tatum, and it feels like they’re starting to get called more frequently. Defenses might even be looking for ways to sell it, and he has to adjust. He was 1 for 6 from the 3-point line in the first half.
▪ Daniel Theis filled in admirably for Williams when he was sidelined for nearly a month following knee surgery, but he was put in a tough spot after playing a total of six minutes in this series entering the night. In his first-quarter stint he badly missed a pair of 3-pointers before ending up on his rear end when Lopez swatted his dunk attempt at the rim. But Theis held up well on defense in the first half, consistently challenging shots along the back line and helping Boston ignite fast-break chances.
▪ The Celtics were outscored with Antetokounmpo on the bench in Game 3, hardly a sustainable approach against a team that is already without injured All-Star Khris Middleton. But they took advantage of his brief absences in the first half Monday, outscoring the Bucks by 9 points in just under four minutes. When he Antetokounmpo was on the floor, Boston did a better job of holding its ground and forcing him to fire away from the perimeter.
▪ The Celtics trailed by 4 points when Brown went to the bench after picking up his fourth foul at the 9:03 mark of the third. Just 23 seconds later, Boston picked up its fourth team foul of the quarter, and the Bucks took advantage of being in the penalty for the rest of the period. With Antetokounmpo leading the way, they pushed toward the rim and either drew contact or found simple chances due to Boston’s hopes of avoiding contact. Antetokounmpo scored inside with 3:15 left to give the Bucks a 76-65 lead.
▪ Brown provided a burst of energy when he returned with about four minutes left, hitting a 3-pointer and scoring inside before rushing upcourt and initially drawing a blocking foul on Holiday, his fourth. But the Bucks, who haven’t had much success challenging calls in this series, were successful with this one. A massive swing, with Brown picking up his fifth foul on the charge and heading back to the bench. The Celtics were outscored by 17 points in the third quarter of Game 3, and 8 in Game 4.
▪ Where would the Celtics have been during these two games in Milwaukee without Horford? He followed up his excellent Game 3 with another productive first half in Game 2. Horford made all four of his shots, provided real resistance in the paint against Antetokounmpo, and went to the break with 11 points, 4 rebounds, and 1 assist. Even though Boston trailed by 1 point at halftime, it outscored the Bucks by 6 during Horford’s 18:36 on the floor.
▪ The Celtics deserve some credit for their perimeter defense, but it was somewhat alarming that they faced a 2-1 series deficit despite holding Milwaukee to 27.9 percent shooting from beyond the arc over the first three games. Even average shooting teams can get hot, and when Milwaukee hit three in a row in the first quarter, it looked like this could be that game. But the Bucks were unable to sustain that momentum, as they entered halftime shooting just 5 for 17 (29.4 percent).
▪ There were plenty of empty seats at the start of Game 2 in Boston because of the 7 p.m. tip that rush hour laughs at. But the Bucks are dealing with Central time zone problems. This game started at 6:30 p.m. locally, and the arena was about half-full at opening tip. The Celtics weren’t able to take advantage of the reduced juice, however.
Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him on Twitter @adamhimmelsbach.