Instant analysis: The Celtics found their stroke from 3, showed some fight, and kept their season alive

The Celtics' Grant Williams and Caleb Martin of the Heat battled for position under the basket in the second quarter.Jim Davis/Globe Staff

MIAMI — On the verge of a humiliating sweep that would have ignited significant questions about this team’s future, the Celtics on Tuesday night kept their season and championship dreams alive for at least one more game, as they rolled to a 116-99 win over the Heat in Game 4 of the Eastern Conference finals.

Game 5 will be played at TD Garden on Thursday night, as the Celtics continue their quest to become the first team ever to overcome a 3-0 deficit in a best-of-seven series.

The Celtics used an 18-0 run to flip a 9-point, third-quarter deficit into a 9-point lead. And after the Heat pulled within 5 at the start of the fourth, a 12-0 Boston surge all but put the game away.

The Celtics, who were pummeled by the Heat’s unusually scorching 3-point shooting at the start of this series, saved their season by regaining their stroke from beyond the arc while turning off Miami’s faucet. The Celtics connected on 19 of 45 3-pointers and the Heat were just 8 for 31.

Jayson Tatum shook off a quiet first half and finished with 33 points, 11 rebounds, and 7 assists to lead the Celtics. Jimmy Butler led the Heat with 29 points but received little help as the outside shooters who had been outperforming hit a cold spell.

Observations from the game:

▪ Al Horford had an unusually lengthy 3-point shooting workout Tuesday morning, clearly focused on snapping out of his long-range slump. He drilled a 3-pointer from the right corner on the Celtics’ first possession and finished the first half 3 for 5, including one miss that went all the way in and out.

Horford had not made more than two 3-pointers in a game since his 5-for-7 night in the Game 3 win over the 76ers in the conference semifinals. It was a bit surprising, however, that he played just 12 minutes, 42 seconds in the opening half. Joe Mazzulla seemed to prefer Robert Williams’s defense on Bam Adebayo. Horford was plus-5 in the first half, while Williams was minus-11.

▪ Neither Tatum nor Jaylen Brown started with the crisp, urgent play that this game required. Tatum committed two turnovers during a 22-second stretch in the first quarter and had four in the half while going 1 for 4 from the 3-point line. Brown had a careless foul on a Gabe Vincent second-quarter 3-point attempt, badly missed a pair of free throws, and just did not appear comfortable.

▪ It’s been a tough stretch for Brown overall, and it was no coincidence that the Celtics’ 14-3 second-quarter run that gave them the lead occurred while he was on the bench. He just hasn’t been contributing at either end. It’s hard to go away from an All-NBA player, but the Celtics have simply needed more from him. The problem is there haven’t been many sterling performances elsewhere, either. Malcolm Brogdon had an uneven first half off the bench, too.

▪ There were questions about whether the Celtics’ effort would wane following the Game 3 blowout that put them on the brink of a sweep. But they at least deserve credit for playing hard in the first half. They had 5 offensive rebounds, 9 second-chance points, and 3 steals, and generally displayed good energy.

▪ Things can really shift with one play. The Heat led, 61-52, early in the third quarter when Kevin Love appeared to cleanly strip the ball from Tatum. It probably would’ve led to a layup and the first double-digit lead. Instead, play stopped, Tatum hit a 3-pointer on the extra possession, and that helped him find his groove. He quickly added another three and a floater as the Celtics seized control with a massive 18-0 run. Tatum had 14 points in the quarter.

▪ Amid all the adjustments and strategies and mind games, these games tend to boil down to which team makes its 3-pointers. The Heat mostly had more shooting luck over the first three games, and on Tuesday the Celtics were able to catch up a bit. Through three quarters, the Celtics were 16 for 37 from long range and the Heat were just 7 for 23. But the Celtics do get credit for making the extra pass and finding some wide-open looks. This time they were just able to connect. Grant Williams was the beneficiary of the extra attention paid to his teammates and he started 4 for 6 from beyond the arc, and his 3-pointer from the top of the key with 42.9 seconds left in the third gave Boston its largest lead to that point, 88-77.

▪ Mazzulla has taken heat for his use of timeouts this season, but he did a nice job Tuesday. On one possession, Brown was trapped in the corner with about nine seconds on the shot clock in a play that was going nowhere. Mazzulla used a timeout, regrouped, and the Celtics got a Tatum 3-pointer. Then Mazzulla used another after the Heat scored the first 4 points of the fourth to pull within 88-83. The Celtics got a nice Tatum 15-footer out of a set play, then a steal led to a Brown dunk.

▪ Grant Williams’s 3-pointers were nice, but his favorite play of the game probably occurred with about nine minutes left in the fourth and the Celtics leading by 9. Butler, who has emerged as his nemesis this series, backed him down and turned for one of his patented fadeaways. And Williams smothered it.