The 76ers are on the brink of elimination.

The Boston Celtics have a series advantage of three games to none after Saturday's 101-98 overtime victory in Game 3 of their Eastern Conference best-of-seven semifinal at the Wells Fargo Center. Game 4 of the series is Monday at Wells Fargo. The Sixers would have to win four straight games to advance.

"I felt like we had control of the whole game, especially when we made our run at the end of the first half," Joel Embiid said. "We felt really good.

"But we made a couple of mistakes at the end. That wasn't good on our part."

The miscues definitely doomed them.

The biggest was an inbounds pass following a timeout at 5.5 seconds left in overtime. Al Horford had just scored on a 4-foot layup to give the Celtics a 99-98 lead. The Sixers called a timeout with the hope of coming up with a play to regain the lead.

But Ben Simmons' attempted inbounds pass to Embiid was stolen by Horford.  The all-star raced down the court and was fouled with 3.0 seconds remaining. He then made both free throws to give Boston a 101-98 cushion.

Marco Belinelli misfired on a three-pointer right before the buzzer, and the Celtics escaped with the win.

"I knew he was fighting for the ball," Simmons said of Horford on the steal. "I was assuming Jo was going to come a little bit further out. Horford read it a little quicker and obviously just went for the ball."

But Simmons also made a decision that ultimately cost the team an opportunity to run a lot of time off the clock.

With his team leading, 98-97, he rebounded Embiid's missed fadeaway with 18 seconds remaining. Simmons missed a short putback instead of dribbling the ball out to the perimeter and taking valuable time off the clock.

"I think it was just natural instinct," Simmons said. " Right next to the rim, it's a shot I take every practice, every day, every game, I take one of those. I missed it."

North Philly native Marcus Morris grabbed the defensive rebound for the Celtics with 14.7 seconds left.  Then the Celtics took advantage of a mismatch on Horford's go-ahead basket.

Embiid picked up Jaylen Brown, who was streaking to the perimeter. That enabled Morris to inbound the ball over top of Robert Covington, who was fronting Horford. Horford jumped out to get the pass behind Covington, came down with the ball, and went back up to score underneath the basket.

Belinelli helped the Sixers overcome a miscue in regulation.

JJ Redick had passed the ball Simmons in the closing seconds of regulation. But Simmons, who has headed toward the paint, wasn't looking for the ball. The ball bounced across the court and into the hands of Celtics point guard Terry Rozier.  He scooped it up and raced down court and found Brown, whose layup gave Boston a 89-87 lead with 1.8 seconds left.

"I was just reading Morris," Simmons said. "He was overplaying me, so I was trying to go behind him for a lob. We did that against Miami [in the first round]. I guess we were all on different pages."

The Sixers called timeout after Brown's layup and got the ball at their end of the court.  That's when  Belinelli hit a long fadeaway two-pointer, just inside the three-point line and in front of the Sixers bench, at the buzzer to force overtime.

An arena employee thought Belinelli's shot was a game-winning three-pointer. So he prematurely fired off a confetti gun, and the teams had to wait until the confetti landed and was swept off the court before starting overtime.

Boston's Jayson Tatum led all scorers with 24 points. Horford had 13 points, six rebounds and three blocked shots.

Embiid paced the Sixers with 22 points, 19 rebounds, one block and three turnovers. However, he wasn't pleased that Horford had zero fouls.

"I don't see how it's possible for someone to guard me and have zero fouls," Embiid said. "So I thought a couple plays it wasn't fair."

He gave Horford credit for making plays and getting the Celtics the win.

"But like I said, I'm too big, I mean I guess it's the playoffs," Embiid said. "It's my first time here. I'm learning, but I'm too big not to be fouled every time I go to the basket or every time I post up."

Aron Baynes, who was also guarding Embiid, picked up five fouls.

Redick had 18 points, while Simmons had 16 points, eight rebounds,  eight assists, four turnovers and two blocks.

It  started off as a solid bounce-back game for Simmons, who had one point and missed all four of his shots in Game 2 on Thursday. Saturday marked the seventh time this postseason Simmons had at least 10 points, five rebounds and five assists. That's the most by a rookie since Hall of Famer Magic Johnson had 10 for the Los Angeles Lakers back in 1980.

It didn't take long for the rookie-of-the-year frontrunner to score more than he did on Thursday. Simmons made his first shot attempt 44 seconds into the game. His second basket, a driving layup, came with 5:41 left in the quarter.  He finished the quarter with four points on 2-for-4 shooting as the Sixers led, 20-19.

Covington had a regrettable performance, scoring one point.  He missed all eight of his shot attempts, going 0 for 5 from the field.

The win was the Celtics' first on the road since March 28 at the Utah Jazz.