“I’ve had like now two or three decent workouts after which I had a little bit of crash, but not this type where I’m like, ‘OK, I can’t get out of bed to make coffee,’” Porzingis said.

On Saturday, Porzingis returned from his eight-game absence and displayed few signs that anything was ever amiss. He made 9 of 16 shots, scored 24 points, and played 31:37 — including the entire fourth quarter — to help the Celtics hold off the Nets, 115-113, Saturday night.

Tests failed to reveal exactly what Porzingis was battling. He said mononucleosis was eventually ruled out, and he believes he had bronchitis “that turned into something heavier.”

“I haven’t been this sick for probably ever in my life,” Porzingis said. “So I was really, for a week really, just laying at home trying to recover. And after that I had lingering fatigue, and I still have it a little bit. But at least I’m now getting into shape to be able to play. But after each workout I was, ‘Boom,’ big crash. I was really, really fatigued. Like, not normal.”

Porzingis said the setbacks were most puzzling and frustrating. He was listed as questionable prior to several games before eventually being ruled out. He was initially pushing to return for the March 8 showdown against the Lakers and put himself through an intense workout the previous day.

“But then the crash I had was, like, historic,” he said. “The next day I couldn’t even get out of bed to go to shootaround. So I was like, ‘All right, now I’m going to lay down to try to get some more rest and maybe I can get going for tonight.’ Then I went to the arena and tried to get some shots up and I was so fatigued. I’m like, ‘I’m not going to be a help out there. I’m just going to hurt the team if I push myself.’”

Porzingis was just 1 for 7 from the 3-point line Saturday, but he was a menace closer to the rim. He had three dunks and seven of his nine baskets came in the paint. His 10-point burst early in the fourth quarter helped steady the Celtics against the charging Nets.

Later, he missed a pair of 3-pointers from the left arc that could have mostly finished off Brooklyn. But his teammates gobbled up offensive rebounds after both shots, and Jayson Tatum eventually found Porzingis streaking to the rim for a powerful one-handed slam.

Celtics guard Payton Pritchard, for one, was unsurprised by Porzingis’s loud return.

“It just shows the skill-set he has,” Pritchard said. “I mean, he’s a unicorn, so he’s an unreal player and obviously when we have him we’re just even more dangerous.”

Porzingis thought he would play about 20 minutes Saturday, but he ended up staying on the court for the entire fourth quarter.

“[Coach Joe Mazzulla] told me mid-fourth, he was like, ‘I’m not going to take you out. So just bite down and let’s go,’” Porzingis said. “So I said, ‘OK, let’s go.’ So I got some sugar in my system and just pushed through.”

Porzingis, who completed a light workout with a team trainer following Saturday’s game, said he felt good but was prepared for lingering fatigue Sunday morning.

Al Horford and Derrick White missed the game to rest, so the Celtics went another day without having their top rotation players available. And Jaylen Brown left in the third quarter with back spasms and did not return.

Pritchard had 22 points and hit 5 3-pointers, giving him an NBA-record 220 off the bench this year. Tatum was just 1 for 7 from the 3-point line but registered 20 points, 8 rebounds and 8 assists.

The Nets sliced a 21-point deficit to 92-89 on a Maxwell Lewis 3-pointer with 8:43 left in the fourth. But Porzingis drew three quick non-shooting fouls that got the Celtics into the penalty just over three minutes into the quarter.

Then over a 40-second stretch he converted a 3-point play that was followed by a 3-pointer from the top of the key, stretching Boston’s lead back to 100-92.

“He looked in good form,” Mazzulla said. “I thought his defensive activity was good. And in the start of that fourth quarter, I thought he put us in a really great position to win and executed down the stretch on both ends.”

The Nets made a late push, pulling within 112-108 on a Ziaire Williams 3-pointer with 56.9 seconds left. After Tatum missed a 3-pointer from the left corner, Keon Johnson banked in a runner to make it 112-110. After two Pritchard free throws, Cam Johnson pulled up for a deep 3-pointer with 4 seconds left that brought the Nets within 114-113.

Pritchard was fouled with 3 seconds left and made the first foul shot before missing the second. But the Nets were out of timeouts and were unable to get off a 3-pointer before time expired.

Adam Himmelsbach can be reached at [email protected]. Follow him @adamhimmelsbach.