Move over Reggie. This was Harden at the Garden. Now, the Sixers just need Embiid.

BOSTON — The man who everybody left for dead arrived at the top of the key with 12 seconds remaining, his team trailing by two. It had already been the finest playoff performance of James Harden’s career, his 33-year-old body delivering 42 points despite carrying the weight of four other players. He was on the road, eight days removed from his most recent game, his team a heavy underdog, the league’s presumptive MVP sitting in street clothes, everybody else on the Sixers sitting on Harden’s shoulders.

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He dribbled to his left, then to his right, then twice between the legs. Then, he did what you expected him to do. He stepped back calmly, rose into his shot, and released a ball so pure you already knew that it was in.

This was one of those performances that you end up remembering long after you start forgetting more important things. Move over Reggie. This was Harden at TD Garden: 45 points, 15 of them in the fourth quarter, the final three lifting a team that did not have a chance to a 119-115 victory.

“I haven’t felt one of those zones in a minute,” Harden said after carrying the Sixers to their first 1-0 lead in the Eastern Conference semifinals since 1986. “It felt really good. You know what I mean? Just to be aggressive and shoot the basketball and do what I want. That felt very good. And I’m capable of doing it. So it felt good. It felt good to make shots, to give ourselves a chance, to be on the road, Game 1, and be aggressive. I mean, we won. That’s all that matters. I’m happy, man.”

Harden didn’t just give the Sixers a chance: he was their chance. I mean, it was over, wasn’t it? Death by a thousand back-cuts. And give-and-gos. And coast-to-coasts. The Celtics made it look so easy in the first half that you couldn’t imagine the final two quarters going any other way. They scored their first six points on off-ball cuts to the basket. They made 14 of their first 15 shots. They scored 24 of their first 33 points in the paint. By halftime, the only resistance they’d encountered was the wind in their hair.

Forget the white board, Doc. What the fellas really need are some reflective vests and orange flares.

Except, the scoreboard said otherwise. That was the mood at halftime, veteran forward P.J. Tucker said. The Celtics had shot 74% from the field and yet the Sixers were down only three.

“We were like, ‘We’re gonna win the game,’” Tucker said. “That’s that confidence in each other. They shot that well and we got the game to three. We can’t let them shoot like, but we’re gonna win the game.”

They did what they needed to do. They talked on defense, called out cutters, contested shots, got back in transition. They got the physicality they needed from Paul Reed. They got the bench minutes they needed from De’Anthony Melton. As usual, they got everything that Tucker had to give.

Most of all, they got a vintage performance from a player who one year ago looked physically incapable of it. Harden came out firing and never really stopped. He hit his first five shots, two of them from three, scoring 12 points in the game’s first five minutes. He hit them from all distances and angles: in the paint, beyond the arc, at the rim.

By the time the fourth quarter arrived, he was in that rarified space that only the greatest of scorers has felt. With 7:40 left in the game, he knifed down the lane off the dribble and exploded toward the rim for a finger roll layup that tied the game at 96-96. The next time down the court, he crossed over a defender and stepped back behind the three-point line to give his team the lead. A few minutes later, he drove to the rim and then whipped a pass back to the top of the arc, where Tobias Harris drained a three-pointer over the defense Harden had just imploded.

“I thought he had the perfect mindset tonight,” Sixers coach Doc Rivers said. “I’m so happy for him. It tells you what he can do on given nights. And then he can be your point guard on given nights. The guy’s a Hall of Famer and all you hear is the other stuff about him. He was fantastic.”

This was him. The Hall of Famer. The perennial MVP candidate. The guy the Sixers acquired at the trade deadline last season. The guy who never arrived to last year’s postseason. The free-agent-to-be who more than a few Sixers fans would be more than happy to see depart.

Somehow, the numbers don’t do it justice. Harden played 39 minutes, attempted 30 shots, hit 17, seven of them from three-point range. His go-ahead three-pointer with nine seconds left gave him 45 points, the highest total in a long playoff career.

This game was a lot of things. But, mostly two. First, it was an example of how much deeper the Sixers are now than they were the last time they began a second round without their most valuable player. Mostly, though, it was a testament to their potential if Embiid can get himself back on the court.

You had to wonder what the big man was thinking as he sat there at the end of the Sixers bench with his hands on his knees. Here it was, the biggest game yet of his best season yet, and all he could do was watch his opponent exploit his absence. Say this for the NBA’s presumptive MVP: Game 1 laid bare just how much he deserves this year’s award. Probably the last two years’ as well.

The Sixers need their big man back. That goes without saying. They cannot win three more games like this. But if he returns? If the sprained knee heals enough that he can simply stand near the basket? Four wins in seven games sounds eminently possible, now that Harden has won them one.

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