Boston Celtics forward Jayson Tatum, left, and Golden State Warriors guard Stephen Curry compete for possession of the ball in the first half of Saturday night’s game in San Francisco. Godofredo A. Vásquez/Associated Press

SAN FRANCISCO — On one sequence late in the fourth quarter, with the Boston Celtics trailing by double digits, Jayson Tatum found himself wide open for a 3-pointer. It clanked off the back of the rim. Following his own miss, Tatum grabbed the long rebound, made one dribble to his left and rose for a layup over Draymond Green.

It went off the backboard, and grazed off the rim for another miss. Tatum put his head down as he jogged back on defense, with the clock ticking down under three minutes to go of the Celtics’ 123-107 loss to the Golden State Warriors on Saturday night.

“It was like, ‘Damn,’ Tatum said. “That was tough.”

It was that kind of night for Tatum, a fitting end for one of his worst performances of the season. The Celtics star has been playing at an MVP-level for much of the year, but in Saturday night’s NBA Finals rematch, he had a case of déjà vu.

His final line: 18 points on 6-for-21 shooting.

“I’ve just got to be better,” Tatum said. “I missed a lot of layups, missed some open 3s, things like that. Nobody to blame but myself. I’ve got to be better to help the team.”

It didn’t help Tatum that he picked up two fouls in the first five minutes of the game, and he never found the right rhythm from there. It was indicative of a team-wide performance, as a league-leading offense finally had an off night. Tatum’s performance represented it. He missed layups. He missed open 3s.

The Warriors made him comfortable all night.

Celtics interim coach Joe Mazzulla deflected the blame.

“He doesn’t have to do anything better,” Mazzulla said of Tatum. “We have to be better. The staff has to be better, I have to be better, we have to put him in better spots in certain moments of the game, feel the game, and get him to a spot where he can make a play for our team.”

Despite the poor outing, Tatum was ready to turn the corner.

“I’m a big believer in great games, bad games, it’s over with,” Tatum said. “There’s nothing I can do about what just happened but get some rest, watch some film and get ready for Monday. That’s just as honest as I can be.”

TIME LORD’S RETURN? Robert Williams III didn’t play against the Warriors, but his season debut is considered day-to-day. The Celtics play at the Los Angeles Clippers on Monday night and at the L.A. Lakers on Tuesday.

“It’s more about just making sure he’s in shape,” Mazzulla said before Saturday’s game. “On a physical standpoint, make sure he’s comfortable from an in-shape basketball standpoint, which is hard to get to when you’ve taken the time off that he has. So I think it’s more about that.”

Williams has yet to play this season after undergoing September knee surgery. While the timeline hasn’t been concrete, Mazzulla confirmed that Williams hasn’t had any setbacks in the recovery process.

Boston has a league-best 21-6 record without its big man, but Williams’ return will unlock a lot of what the Celtics want to do defensively. He’s a huge piece of the equation as the team tries to return to the NBA Finals.

GRANT WILLIAMS was ejected for the second time this season in the closing moments of Saturday’s game.

The ejection occurred with 1:52 remaining. Mazzulla called timeout to pull his starters out of the game, and Williams punched a loose ball after the timeout was called. The ball flew into the stands, resulting in a technical foul and an automatic ejection, according to the officials.

Williams appeared surprised by the harsh penalty, but his protests were not heard given the NBA’s clear rules on throwing a ball into the stands. The power forward finished with four points, two rebounds and a steal in 31 minutes.