Marco Belinelli's shot with 1.7 seconds left in regulation was supposed to be a walk-off three-pointer.

The game was supposed to be over — that was the plan. Sixers coach Brett Brown left the court, thinking the plan had worked. Even the man with his finger on the confetti trigger thought that it was over, that the Sixers had won Game 3.

But that's not what happened.

Out of the Sixers' final time-out, Belinelli, guarded by Terry Rozier, ran around the arc to the right side of the basket. As he passed Ersan Ilyasova and Jayson Tatum, Rozier slipped and fell to the floor, giving Belinelli just enough room to get off a turnaround jumper off the inbound pass from Ben Simmons.

"I was open, I take that shot and make it, and everybody was happy," Belinelli said. "But, at the end of the day, we lost the game, so who cares."

It was a shot Belinelli has practiced, a shot that he is known for making. This time though, his foot was just over the three-point line. The bucket was ruled a two-point shot, and after a review the call was confirmed. The game went into overtime and the Sixers lost to the Celtics 101-98.

"Belinelli hit a heck of a shot," Celtics coach Brad Stevens said after the game. "But you move on and get ready to play the next five minutes."

That's exactly what Boston did.

Just 40 seconds earlier in regulation, Belinelli drove down the lane and drew contact. The play gave Celtics guard Marcus Smart his sixth foul — a break for the Sixers — and Belinelli hit both free throws for an 87-85 lead.

On the next possession, a fan lamented that Belinelli was guarding Jayson Tatum. The veteran's defensive limitations had been exploited in the first game of this series. But it wasn't Tatum who got free.

Jaylen Brown tied the game out of a timeout with 24 seconds remaining. On the other end, an errant pass by JJ Redick was picked up by Rozier, who passed to Brown on the fast break, giving the Celtics a two-point lead with 1.7 seconds on the clock.

That turnover was one of the plays the Sixers head coach said he wished he could have had back.

In the overtime period, Belinelli was the first to score for the Sixers on another long two, this time from Joel Embiid. With just under two minutes left, Belinelli stripped an offensive rebound from Tatum, doing everything he could to give the Sixers the break they needed.

After a Simmons drive and score with one minute left, it looked as though the Sixers were in a good spot, but the mistakes started mounting.

Embiid turned the ball over on a bad pass intended for Belinelli with 46 seconds left. It was another mistake that the Sixers couldn't take back.

Leading by just one point, Embiid missed a jumper, and Simmons pulled down the offensive rebound, but instead of pulling it out and using some clock, he went for the put-back and missed.

The Celtics continued to execute on their end, while the Sixers came up empty. A final turnover put the Sixers in another walk-off situation. But the Sixers had used up all their luck, all of their timeouts, and Belinelli couldn't save them.

"Too many stupid mistakes," Belinelli said when asked what went wrong.

On the final play, he was forced to heave a desperation three off of a full-court inbound play. The shot hit the rim and bounced away.

"We got our look out of it," Brown said of the play. "It wouldn't have surprised me if he made that shot. He makes those types of shots."

The Celtics closed the game with a 7-0 run to win Game 3 and take a 3-0 series lead in the Eastern Conference semifinals.