The Sixers were out of gas, out of luck, out of time. Now, they’re alive.

The best seconds in sports are the ones that unfold like this. The clearout, the pick, the drive, the dish, the sound of the buzzer, the sound of the swish, a beat of the heart between the two, separating silence and bedlam.

Bedlam reigned at the Wells Fargo Center on Sunday afternoon. The Sixers watched their life flash before their eyes and then realized that they were still breathing. Moments like these have been known to change men. Maybe they can have a similar effect on teams.

If the Sixers end up where they want to go and carrying a city along with them, everybody will look back on Game 4 of the Eastern Conference semifinals as the moment that launched them. You can’t say that about a lot of games in an NBA postseason, but you can certainly say it about this one, a 116-115 overtime win over the Celtics that felt like its own self-contained series.

» READ MORE: Philly Tough: Joel Embiid’s heroic game & James Harden’s bounce-back evens series. Now, do it again.

It ended with Marcus Smart in the air and the ball in his hands and the border of the backboard bathed in red. This was 19 seconds after James Harden drilled the game-winner, and 38 seconds after Jayson Tatum drilled a go-ahead shot of his own. It was five minutes after Smart came up short at the end of regulation, which came 16.1 seconds after Harden tied it with a floater the lane, which came after two quarters of basketball in which the Sixers seemed destined to collapse upon themselves.

Do not underestimate the significance of being the last team standing after a game like this.

“It was a must win for us,” said Harden, who scored 42 points. “Easy. A must win.”

They believed that even before Game 4 turned into an epic. After back-to-back losses and a 2-1 series deficit, the Sixers followed a spirited off-day film session with one of their best offensive halves of the season. They did all of the things they knew they needed to do, all of the things they hadn’t done in Games 2 and 3. They were playing off of their stars instead of through them. They were moving the ball on offense, cycling to it on defense, pouncing on it whenever it was up for grabs.

This is how basketball goes when it’s going good. There’s an energy that flows from one phase of the game to the other and seems to level up everybody in a given jersey by an extra five or 10 percent.

You saw it late in the second half, when Tyrese Maxey held his ground against Jaylen Brown and Jayson Tatum in back-to-back possessions, forcing a couple low-percentage shots that ended up as defensive rebounds. You saw it early in the third quarter, when Georges Niang knocked a ball loose and Harden went to the court to force a jump ball that he then won. You saw it late in the third quarter, when Tobias Harris saved a turnover by snatching a lazy Embiid pass from a defender, setting off a scramble play that led to an open corner three by Niang. You saw it the next time down the court, when an energized Harris knocked down a pull-up three-pointer to give the Sixers a 90-75 lead.

“That’s one of those things in Game 2 and even last game that we kind of got away from,” Harden said. “The ball’s gonna find the open guy. When we space the floor and do the things we need to do, it’ll find the open shot.”

That being said, it goes the other way too. If the Sixers are going to come back to Philly with a 3-2 lead, it isn’t going to happen the way they tried to do it after taking a nine-point lead into halftime. For most of the second half, that’s the direction it went. There were too many stagnant possessions, too much one-on-one, not nearly enough of the spacing and pace that the Sixers had generated in the first half. The ball turned from a rolling stone to a green glob of moss.

As is often the case, Joel Embiid was setting the tone. This time, the note was flat. With just over five minutes left, he tried to take Al Horford one on one and ended up getting blocked at the rim. A couple of minutes later, Horford blocked a pull-up attempt. He was gassed. The whole building knew it. Crucially, that included the Celtics.

With 1:49 left, Embiid made a nifty move to get past Horford on the elbow then attempted to Eurostep around Smart, who’d established position just outside the restricted area. Embiid couldn’t shift his momentum in time to avoid contact, and was whistled for the offensive foul. A minute later, he tried to take Smart to the hole and ended up spinning into another block by Horford. On the Celtics’ first possession of overtime, Embiid couldn’t even get off the ground to contest a Jayson Tatum layup.

“We got tired, honestly,” Rivers said, “and it’s tough to draw up a play when everybody’s fatigued. Let me say that.”

They were out of gas. They were out of answers. But they were not out of will: Harden carrying them on his much-maligned shoulders, Embiid summoning what little he had left to hit a couple of crucial free throws and then toss a kick-out from the paint to set his co-star up for the game-winner.

And then it was over. Finally, officially, over. Buckle up, everybody. We’ve got ourselves a series.

» READ MORE: James Harden’s game-winner lifts Sixers to wild 116-115 overtime win to even series with Boston Celtics