LeBron James insisted there is no reason to worry despite the Cleveland Cavaliers losing to the Boston Celtics in game one of their NBA Eastern Conference final.

The Celtics drew first blood on Sunday, winning 108-83 against James and the Cavaliers.

There was no concern from James after the Indiana Pacers jumped out to a 1-0 and 2-1 playoff series lead last month before the Cavaliers rallied to win the first-round matchup.

And James is remaining calm again, telling reporters: "I have zero level of concern at this stage.

"I didn't go to college so it's not March Madness. You get better throughout the series, see ways you can get better. I've been down 0-1, been down 0-2. There's no level of concern."

Cleveland's 25-point loss on Sunday is the second-largest game-one loss by a James team in his playoff career.

James was guarded by Marcus Morris on 24 plays, finishing with 15 points on five-of-16 shooting.

"I've seen every [defensive] coverage," James said. "For me, game one has always been a feel out game if you follow my history. I got a good sense of the way they played me today and how I'll play heading into game two."

The Cavaliers looked to be sleepwalking against the Celtics while shooting just 36.5 per cent from the field and 15.4 per cent from three-point range.

"Three-point shots are a part of our DNA. That's what makes us the best team we can be," James said. "Even early on, we had some wide one looks that just didn't go. J.R. [Smith], Kev [Kevin Love], G-Hill [George Hill], they had some great looks. We're absolutely okay with that."