In a scramble to the finish, Jayson Tatum’s clutch layup at the buzzer lifts Celtics in Game 1, and other observations

The Celtics' Jayson Tatum (right) is pumped — not so, Kyrie Irving (left) — after he hit the winning layup at the buzzer.Jim Davis/Globe Staff

With Kyrie Irving sparking a big Nets fourth-quarter comeback and the Celtics in danger of dropping the first game of this opening-round playoff series, Boston regrouped before it was too late.

Kevin Durant missed a tough jump shot with 14 seconds left that would have given his team a 4-point lead. The Celtics elected not to call timeout, and a scattered possession ended when Marcus Smart drove toward the hoop and found Jayson Tatum for a layup at the buzzer, sending Boston to a 115-114 win Sunday at TD Garden.

When it became clear that the Celtics and Nets would meet in a first-round series, it instantly became the most tantalizing matchup of these playoffs. And if Sunday’s game was any indication, it will live up to the hype.

Tatum finished with 31 points and eight assists and Al Horford added 20 points and 15 rebounds for Boston. Irving finished with 39 points.

The Nets trailed by as many as 15 points in the second half and were behind by 11 at the start of the fourth quarter. But Irving sparked their 15-2 surge to start the fourth and the Nets led by as many as five.

With the score tied at 111, Irving drilled a 3-pointer that gave his team a 114-111 lead with 45.8 seconds left. Brown attacked for a layup that pulled Boston within 1, and Durant’s tough jumper was off. Horford pulled down the rebound and Smart and Tatum took care of the rest, giving Boston 1-0 lead in this best-of-seven.

Observations from the game:

▪ The Celtics led, 96-85, at the start of the fourth, and with Durant on the bench, it was a good opportunity for Boston to stretch its lead. Instead, Irving took over, drilling a pair of 3-pointers and hitting a layup to spark a 15-2 Brooklyn run. Irving collected his fourth foul early in the period and it was obvious he had no intention of collecting his fifth, as he let Celtics blow past him throughout the fourth. It almost didn’t matter, though, because at the other end, he did not stop scoring.

▪ Smart had a team-high four 3-pointers, and when he caught a pass at the left arc with 3.5 seconds left, it sure seemed likely that he would go for his fifth. He was open, and there were no clear options elsewhere. Bruce Brown seemed to expect that Smart would launch a shot, as he flew past him while going for a potential block, giving Smart a path to the hoop. Even then, given the time, a floater would probably be his best option. But Tatum noticed that three Nets had their back to him and their eyes on Smart, so he sprinted from the top of the key and Smart found him just in time. It was good awareness by both Smart and Tatum.

▪ The Celtics’ stars were scuffling at the start, but Al Horford ensured that the team would stay afloat. The veteran big man hit a pair of 3-pointers, ran the court and threw down an alley-oop on a fast-break, and came up with a steal before he was fouled. Afterward, he walked toward the crowd and subtly flexed, much to the delight of the fans. He’s been waiting for this opportunity after two essentially lost years, and he really believes this season can turn into something special.

▪ Brooklyn’s offense was disjointed early, partly because of Boston’s swarming, switching scheme. The Nets committed six turnovers in the first six minutes, with the Celtics using quick hands to swipe the ball away on drives.

▪ The Nets also committed seven early fouls, but the Celtics quickly caught up to them in that department in a first quarter that turned into a whistle-filled slog. In all, there were 18 total fouls called in the period, the most in the first quarter of any game this season. Once a foul tone is set, it can be difficult for referees to escape it. If a touch foul is called at one end, it has to be called at the other. But it did not make for enthralling viewing.

▪ The rush of fouls also resulted in some foul trouble. Celtics center Daniel Theis picked up his third early in the second quarter and sat for the rest of the half, and Boston caught a break a couple of minutes later when Horford appeared to foul Kevin Durant — it would have been Horford’s third — but the foul was ultimately given to Marcus Smart. Nets center Andre Drummond collected his fourth late in the second quarter.

▪ Jayson Tatum had a difficult start on offense but stayed engaged by flinging some timely and accurate passes. He did well to escape double teams and had seven first-half assists. Then late in the second quarter he began to find a rhythm as a scorer. He hit a deep 3-pointer, poured in a tough baseline fadeaway over Durant, and got to the rim by attacking Nic Claxton.

▪ Durant struggled in the first half, going 2 for 10 from the field. He was clearly and rightfully the focus of Boston’s attack and he appeared frustrated at times. Late in the second quarter he finally had an opening for a drive and a layup, but Smart stepped in and did an excellent job of staying vertical and challenging Durant at the rim, forcing an awkward miss.

▪ With the score tied at 63 early in the third, the Celtics took control with a 9-0 run that was sparked by Smart and included one awful play by Brooklyn. After a pair of Theis free throws, Kyrie Irving took the ball to inbound it from the baseline, but all four of his teammates ran upcourt. Irving put his arms in the air as if to say, ”A little help?” A pair of teammates finally started heading back in his direction, but Irving bounced a long, careless pass that Smart gobbled up before soaring in for a dunk. Smart followed with three 3-pointers as Boston stretched its lead to 15. It was surprising that Nets coach Steve Nash didn’t call a timeout after that messy play to regroup.

▪ The Nets whittled away at the 15-point deficit in the third and appeared to have an easy two-on-one fast break in the final minute that would have pulled them within 4. But Boston punched back behind its defense, which has been a constant this year. Brown swooped in and blocked that shot, and Tatum blocked a Durant attempt on Brooklyn’s next possession, and by the end of the third the lead was back to 96-85.

▪ There’s been a lot of buzz about Nets point guard Ben Simmons potentially making his season debut during this series. It’s certainly possible Brooklyn just didn’t want him to show anything that could be endlessly dissected in the coming days. But during pregame warm-ups, Simmons hardly looked like a player who is a week away from playing in a real game. He spent about a half-hour just standing still and tossing passes to his teammates.

▪ For the old-school crowd: The moments before the opening tipoff generally look like family reunions, with starters on both teams exchanging hugs and handshakes. But the start of this game did not feel like that. There were a few courteous head nods between the two sides, but that was about it. Irving usually has lengthier greetings because these are his former teammates, but it didn’t happen in this one.