Kelly Olynyk scored 26 points from the bench as the Boston Celtics outmuscled the Washington Wizards 115-105 to clinch their Eastern Conference semi-final series on Monday.

Olynyk produced a superb display of shooting from distance as Boston pulled clear of the Wizards in the late stages of the game to take the series 4-3 and set up a Conference final clash with Cleveland.

Isaiah Thomas topscored for the Celtics with 29 points and weighed in with 12 assists while Al Horford (15), Jae Crowder (14) and Marcus Smart (13) also made double figures.

But it was Olynyk’s remarkable display off the bench that proved decisive as the Celtics clinched their first Eastern Conference finals berth since 2012.

“A friend called me and said ‘Be at your best when your best is needed’ and my best was needed tonight,” Olynyk said after the win.

“Everybody gave it their best and it turned out for us tonight,” added the 26-year-old Canadian power forward.

Olynyk described the series win as a “a team effort.”

“It was hard work, that was a tough seven-game series. Both teams played tough — we just kind of outlasted them at the end there. We’re lucky to move on,” Olynyk said.

Boston now host NBA champions Cleveland on Wednesday. “We’ve just gotta keep playing our brand of basketball and we’ll see what happens,” Olynyk said.

The defeat marked another frustrating end for Washington however.

Bradley Beal exploded for 38 points but it was not enough to overcome the Celtics rugged defense. Otto Porter Jr added 20 points while John Wall and Markieff Morris scored 18 each.

No other Washington player made double figures, highlighting the team’s threadbare relative lack of options off the bench. Wall meanwhile made only one of eight attempted three-pointers.

• From AFP