T.J. McConnell was assertive after starting in the biggest game of the season with the 76ers on the brink of playoff elimination.

And because he started, the Sixers get to play Game 5.

They fed off his grit in Monday's 103-92 victory over the Boston Celtics in Game 4 of the Eastern Conference semifinals at Wells Fargo Center. Game 5 is set for Wednesday at the Celtics' TD Garden. With a commanding  3-1 lead, Boston could clinch the best-of-seven series with a win Wednesday.

"I think everybody fed off that energy," said the Sixers' Ben Simmons.

However, that was the furthest from the Sixers' mind during the game. They were too busy taking it to the Celtics.

McConnell, who started in place of Robert Covington, provided the spark.

The point guard scored a career-high 19 points on 9-for-12 shooting. He also added seven rebounds and five assists while playing a career-high 38 minutes, 57 seconds. Oh, and the Pittsburgh native dived for loose balls, played solid defense, had no turnovers, and graded out with a plus-18.

Simmons (19 points, 13 rebounds, five assists) and Joel Embiid (15 points, 13 rebounds) both had double-doubles for the Sixers. Dario Saric had his best game of the series, scoring a game-high 25 points.

Jayson Tatum had a team-high 20 points for Boston, while North Philly native Marcus Morris added 17.

The Sixers had a commanding 18-point cushion in the fourth quarter before cruising to the 11-point victory. They shook up their starting lineup as a way to give themselves a lift.

McConnell started at shooting guard alongside Simmons in the backcourt. Meanwhile, JJ Redick, the normal shooting guard, slid to small forward in place of Robert Covington, who came off the bench.

Covington was solid in Game 2, but he struggled mightily in Games 1 and 3, shooting a combined 0-for-14 in those matchups. He finished with three points on 1-for-7 shooting — including going 1 of 3 from long range — on Monday.

"There's an injection of energy that you immediately know that you are going to get with him," Sixers coach Brett Brown said of starting McConnell.  "You heard me talk for the previous 48 hours, making sure that our spirit didn't take a hit."

Looking for a way to motivate his team, Brown reminded them of their successful season. He also wanted them to "retain, maintain, increase their spirit."

"There's no better player to help catapult the start of the game with that mind-set than T.J." Brown said. "The decision was based on a lot of other things, but that is the main thing. Just the energy."

McConnell learned from assistant coach Lloyd Pierce that he would get his first start since Nov. 25  — and second of the season — while walking on the court for the pregame walk-through.

"I just didn't expect it," McConnell said. "I thought they were still going to go with Cov. He's a big reason why we are where we are right now.

"Like I said, when my number's called. I just try to help the team as best as I can."

The McConnell and Simmons backcourt was successful from the start.  On a fast break, McConnell delivered a bounce pass to Simmons, who finished the play with a dunk. That put the Sixers up, 8-5, with 7:14 left in the first quarter.

Philly had an 11-7 advantage before Covington subbed out McConnell at the 6:07 mark of the quarter.

Covington, however, missed both his shot attempts before leaving the game a minute into the second quarter after picking up his third foul.

In regards to fouls, the Celtics were called for 16 of them in the first half and 28 for the game. Tatum, Morris, Marcus Smart, and Jaylen Brown all had three apiece before intermission.

Things got heated after Terry Rozier was called for an offensive foul after reaching around Redick's neck with 2:27 before intermission. Rozier held onto the ball, Embiid went to grab it from him and the Celtics point guard tried to play keep-away while arguing the call with the referee. So Embiid went for the ball again, and Rozier shoved the all-star center.  The Celtic then appeared to try to shove Embiid again while they were locked up.

After a long review, the referees called double technicals.

"He tried to punch me twice," Embiid said. "Too bad he's so short that he couldn't get to my face.

"I didn't understand why it was a double technical, because I was trying to get the ball. He was the one trying to swing."

The tussle appeared to motivate Embiid. He buried a three to give the Sixers a 43-38 lead once play resumed. And his dunk while cutting to the basket right before the buzzer gave the Sixers a 47-43 halftime advantage.

The Sixers went on to take a commanding 86-68 lead with 9:02 remaining in the game. The sellout crowd of 20,936 chanted "T.J.! TJ ! TJ!" when McConnell was subbed out 29 seconds later.

McConnell said it was gratifying to have his teammates and the crowd feed off his energy.

"But we can't be satisfied with this," McConnell said. "We've got to try to go get one in Boston and come back in front of these great fans."