BOSTON – The Boston Celtics inserted Marcus Morris into the starting lineup for Game 1 of the Eastern Finals Sunday afternoon, hoping that he would give them a versatile boost on both ends of the floor against the Cleveland Cavaliers.

The veteran forward took full advantage of his promotion by putting forth his best all-around effort of the postseason, while helping the C’s cruise to a 108-83, series-opening win.

Morris tied his postseason high of 21 points on 7-of-12 shooting from the field and 3-of-4 shooting from long range, while also corralling a career playoff-best of 10 rebounds. After experiencing a bit of an offensive slide during the second round against Philadelphia, it was exactly the type of leaf-turning game Morris was looking to have to open up the new series.

“I was just playing in the flow of the game,” Morris later reflected. “I got a lot of open shots, a lot of easy shots. We just did a great job of moving the ball.”

Despite the fact that Morris shot just 30.5 percent during the last series, coach Brad Stevens was confident that his tenacious forward would be able to break out of his funk and return to his role as a key offensive producer.

“He’s a really good shooter. He’s a good offensive player,” said Stevens. “I never worry about shots not going in game to game. He’ll make shots.”

As impressive as Morris’ offensive game was, his defensive effort was even more outstanding.

Morris found himself guarding LeBron James on 24 possessions and allowed just five points in the process. That effort played a huge role in helping the Celtics limit James to playoff-low of 15 points on 5-of-16 shooting, including 0-for-5 from 3-point range.

Seeing Morris step up on the defensive end impressed his teammates, but at the same time, they were not the least bit surprised by it.

“Marcus is one of our leaders, and he’s been a presence since the first day he got here,” said fellow veteran Al Horford, who contributed to the win with 20 points, six assists and four rebounds. “I think that taking on this challenge is something that we expect out of him. We have his back out there. We were [defending James] as a unit. It’s not all on [Morris]. But you do have to give him credit for his focus and his commitment to the team.”

Having such focus and commitment is something that the Celtics front office expected from Morris when they traded for him last summer. They had seen his drive and his passion for the game while he was playing for the Detroit Pistons and believed that those factors, coupled with his experience, would greatly benefit the team.

“The biggest thing is that he’s been in the league a long time, and he’s done a lot of good things,” said Stevens. “He’s been a good player for a long time. He was very hard for us to play against in Detroit, and we had high expectations for him coming into the year. He certainly has met those and continues to play great.”

The Celtics will need Morris to continue to play great in order for them to carry their success over into Game 2. He’ll likely be called upon to step into a starting role again Tuesday night, and he’ll look to take full advantage of the opportunity just as he did during Sunday’s series-opener.