Observations after the Nets fought hard in Game 4, but the Celtics closed them out anyway

Jayson Tatum led the Celtics with 29 points despite spending much of the fourth quarter on the bench due to foul trouble (and eventually fouling out).Jim Davis/Globe Staff

NEW YORK — With a sweep within sight and an opponent seeming to lose confidence by the minute, the Celtics appeared poised to finish off the Nets and send them into summer without much trouble.

But there was a brief plot twist when star Jayson Tatum fouled out with 2 minutes, 48 seconds remaining and his team leading by six points. Emboldened, the Nets scored five quick to pull within 1 and put a jolt into a relatively sleepy playoff crowd at the Barclays Center.

Then, with Tatum watching from the bench, his teammates picked him up, as they once again made big plays in big spots and secured a wire-to-wire, 116-112 win that ended this series far sooner than most pundits believed.

The Celtics advance to the conference semifinals, where they will face the winner of the first-round series between the Bucks and Bulls, which Milwaukee leads, 3-1. Game 5 is Wednesday in Milwaukee.

Tatum finished with 29 points, Jaylen Brown scored 22, and Marcus Smart added 20 points and 11 assists. Kevin Durant had 39 points on 31 shots to lead Brooklyn.

Tatum looked poised to put away the Nets at the start of the fourth, when he threw down a dunk and then stepped into a 3-pointer from the top of the key that made it 95-86 with less than nine minutes left.

But on Boston’s next possession, he drove and committed his fifth foul charging into Brooklyn’s Blake Griffin. The Nets pulled within 102-99 with Tatum on the bench after Goran Dragic banked in a 3-pointer from the top of the key with 5:23 left, but Jaylen Brown answered with a three-point play.

Tatum came back in, but fouled out on an offensive foul with 2:48 left and Boston leading, 109-103.

Kyrie Irving hit a 3-pointer and Durant added a 14-footer with 1:28 left, pulling Brooklyn within 109-108. With the shot clock running down, Brown briefly lost the ball along the baseline, but regained possession and found himself open for a layup.

Durant missed a potential tying 3, then a possession later was fouled with 22.2 seconds left, but made just 1 of 2 free throws. The Celtics’ counter-attack came quickly, with Smart rushing upcourt for a layup that missed. That could have been disastrous, but Al Horford swooped in and converted, making it 113-109 with just 13.7 seconds to play.

Durant back-ironed another 3-pointer, and the celebration was on.

Other observations from Game 4:

⋅ There are rarely significant moments in the opening minutes of the NBA game, but this felt like one: With Boston leading, 8-5, Curry stripped Tatum and came up with the loose ball with a clear path ahead. There was some contact by Curry and then some by Tatum. But a late whistle on Curry stopped the break and also gave him his third foul, sending him to the bench for the rest of the quarter.

Fouls have been an issue throughout this series, and the Nets were slowed by their own hacking, as they committed 10 first-quarter fouls.

⋅ In the first quarter, the Celtics made just 39.1 percent of their shots, allowed the Nets to connect on 55.6 percent of theirs, committed five turnovers, and did not get a basket from Tatum. Still, Boston grabbed a 30-26 lead.

Nic Claxton’s free-throw shooting was a big reason for that. The backup center was 0 for 6 from the foul line in the opening half and missed his first 10 of the game, extending his miserable stretch of free-throw shooting. The Celtics eventually deployed a hack-a-Clax strategy when Payton Pritchard entered the game to foul the big man midway through the third quarter, but he made his 11th and final try of the day, eliciting a roar from the crowd.

⋅ Celtics fans have seen this before, but Irving certainly did not seem very engaged during the first half. He looked like a player who understood that the season’s end was near, and that there was no reason to prolong it.

⋅ Grant Williams provided a huge offensive lift for the Celtics in the opening half. He was 4 for 5 from the 3-point line, with Brooklyn leaving him as open as teams did at the start of this season, before they believed his solid shooting was a real thing.

But his finest moment of the first half came on defense. After drilling a corner 3-pointer, Williams was matched up against Durant along the left baseline. He stood his ground and pushed back Durant’s first attempt to attack. Then he stripped the ball away and it caromed out of bounds off of Durant. Celtics coach Ime Udoka walked over and gave Williams a powerful high-five for his efforts.

⋅ Robert Williams, who was playing in his second game after missing nearly a month due to left knee surgery, appeared a bit tentative in the opening half. He never had a chance at one ambitious alley-oop pass thrown his way. Then he had a chance at an easy putback that he’d normally slam home, but instead he caught the ball, came down with it, and missed a pair of layups. It’s probably just rust, but his usual burst hasn’t really been there so far.

He played only 14 minutes, finishing with 3 points, five rebounds, and four fouls.

⋅ The Nets have one of the more apathetic fan bases in the NBA, partly because most New Yorkers are lifelong Knicks fans and it’s tough to just switch allegiances when a different team just arrives in the city. The crowd was unusually loud and engaged in Game 3 on Saturday, but much of that energy seemed to be sapped Monday. The 3-0 deficit washed away some of the excitement, and probably made it easier for Celtics fans to find their way into the arena, too. There were certainly more of them.

Last game, Tatum received scattered ‘MVP’ chants in the final minutes when the game’s outcome was decided. On Monday, they arrived in the first quarter.