Boston Celtics forward Marcus Morris was not happy with his game-three performance against the Cleveland Cavaliers, describing his defense on LeBron James as "s***".

Morris and the Celtics were no match for the Cavaliers, who reduced Boston's series lead in the NAB Eastern Conference finals to 2-1 via Saturday's 116-86 rout in Cleveland.

There was plenty of blame to go around after Boston's lacklustre display but Morris accepted a portion of the responsibility.

Cavs superstar James scored 27 points and tallied 12 assists in game three.

"Personally, I think I did a s*** job defensively with LeBron. He was too comfortable when I was guarding him," Morris said. "I made myself very vulnerable on screens and wasn't disciplined. We can't have that in a game of this magnitude, and it showed. They did a great job of exposing that. Personally, I think I have to do better.

"I watched the first two games and how we defended them and how I defended [James] personally and, like I said, [game three] I just thought I did a terrible job.

"I made myself very vulnerable and got screened a lot, and he made his space. He's a great player and that's what he does, so we have to fix that."

Morris added: That [Celtics] team we saw [in Game 3], I'm 100 per cent sure it won't be the same team on Monday.

"After watching film, we did a lot of things that caused us to be in the position that we're in. I said before, control the controllables, and we didn't do that."