Philadelphia’s Joel Embiid, left, and P.J. Tucker celebrate during Game 4 of the Eastern Conference semifinals Sunday against the Boston Celtics. The 76ers tied the series with a 116-115 overtime win. Matt Slocum/Associated Press

PHILADELPHIA — James Harden had a new friend he called his good-luck charm in the arena and the grit he needed to turn in a vintage effort – in the form of tying and winning shots – for the 76ers.

After looking down-and-out in the previous two games, Good Game James saved the 76ers in Game 4.

Harden hit a floater to tie the game with 16 seconds left in regulation and buried a go-ahead 3-pointer with 18 seconds remaining in overtime, finishing with 42 points to help the Sixers stave off a wild Boston Celtics comeback in a 116-115 victory on Sunday.

“I just want to win,” Harden said. “Today was do-or-die for us.”

The 76ers tied their Eastern Conference semifinals at 2-2, with Game 5 set for Tuesday in Boston.

Harden won the game in front of John Hao, a paralyzed Michigan State shooting survivor who developed a long-distance friendship with the 10-time All-Star. Harden invited Hao to a game as soon as he was able to travel.

“He’s strong, he’s bouncing back, he’s recovering very well,” Harden said. “I feel like it’s my job to give him that light, that smile that he deserves. Hopefully today was one of those days where he can smile.”

Harden waved over Hao and signed his game-worn sneakers moments after Marcus Smart’s potential winning 3-pointer was a tick too late. The 76ers are now guaranteed to return home for Game 6 on Thursday.

Jaylen Brown said his poor defensive read when he ditched Harden to double Joel Embiid was a pivotal moment.

“It’s a gamble at the wrong time and a big shot by James Harden,” he said. “That’s my fault. I take full accountability.”

Smart and Jayson Tatum keyed a Celtics rally from 15 points down late in the third quarter.

Boston’s fun began in the fourth when Smart and Brown buried consecutive 3-pointers and Tatum attacked the rim for a bucket that wiped out an eight-point hole in 90 seconds. Al Horford put the Celtics ahead 98-96 – after Tyrese Maxey had his shot blocked at the other end – and shimmied as boos rained on him.

Yes, the 76ers had home court, but fans tensed up as memories of all those second-round exits since 2001 stirred inside the building. Smart and Malcolm Brogdon hit consecutive 3s for a 105-100 Boston lead.

But it was P.J. Tucker, the heart and guts of the Sixers, who again did the dirty work with an offensive rebound and a bucket. He was fouled and made the free throw with 1:05 left to the tie game and give the Sixers new life.

The Sixers were on the brink of defeat numerous times over the final 17 minutes, none more than when Embiid crashed into Smart on a driving, one-handed bank shot with 1:49 left in overtime and was whistled for an offensive foul. The play was reviewed and the call stood. Boston kept its 112-111 lead

Embiid, the NBA MVP who had 34 points and 13 rebounds, kept his composure and eventually got to the line for two free throws that gave Philadelphia a one-point lead with 59 seconds left.

Tatum, who struggled to score early but finished with 24 points, 18 rebounds, six assists and four blocks, hit a step-back 3 for a 115-113 lead.

“Jayson Tatum’s 3 was awful that (a push-off) wasn’t called,” 76ers Coach Doc Rivers said. “You’ve got to call that play. I know it’s a big play and I’m a big fan of refs not deciding (the game), but it could have decided the game.”

Brown scored 23 points and Smart had 21.

Brown, though, took only three shots in the fourth quarter and none in overtime.

“I guess I’ve got to demand the ball a little bit more,” he said. “I thought good things happened when I had it in my hands. I thought our offense was OK. We chipped away, we made big-time shots, we got great looks all game long. We just came up short in the end.”

Harden played in Game 1 like he was still the MVP and dropped 45 points to spur an upset road victory. Then, his game disappeared and he played two of the worst games of his career, going 5-for-28 combined in Games 2 and 3.

He regained his form in Game 4, hitting all three of his 3-point attempts in the first half while scoring 21 points – five more than his Game 3 total. Embiid was as potent as he could be on one good knee and had 19 points and 11 rebounds to help the 76ers lead 59-50 at the break.

“Tonight, playing a lot of minutes kind of got to me at the end,” Embiid said. “We made the plays when we needed. PJ with the big and-1. Obviously, the James shot. I thought we stuck with it. But that’s been us all season long. We stick together and fight through everything.”

TIP-INS

Celtics: Horford also made only one basket in the first half. Brown tried to help with a 7-of-11 effort for 16 points.

76ers: Embiid and Harden are the first Sixers teammates with 30 points each in a playoff game since Embiid and Seth Curry did it in June 2021 against Atlanta.