So much for the Cavaliers being rusty.
LeBron James embarrassed every defender Boston threw at him and Cleveland picked up where they left off after a 10-day layoff, rolling to a 117-104 victory in game one of the NBA Eastern Conference finals.
James had 38 points, nine rebounds and seven assists in 41 minutes on Wednesday night.
Kevin Love added a playoff career-high 32 points and had 12 rebounds to help the Cavaliers improve to 9-0 in the first three rounds of the playoffs.
They opened 10-0 last season en route to their first NBA title.
"It was our two bigs that set the tone - Kev and Double-T (Tristan Thompson), they were phenomenal," James said.
"I saw it in Kev this morning. I knew what type of game he was going to have. So he came through for us."
But there's no denying it has started with James, who has scored at least 35 points in five straight games.
Cavaliers coach Tyronn Lue said James' efficiency continued to make things easier for everyone on both ends.
"He's playing at a high level. And that's the reason why we're riding him so much," Lue said.
"When LeBron's playing at that level other guys just have to be solid and we have a good chance to win."
Game 2 is Friday night in Boston.
James and the Cavaliers raced to an early lead and were never threatened.
"You can't dig yourself in a big hole like that against them," Celtics coach Brad Stevens said.
James scored at will in the first half and the Cavs built a 26-point lead.
Avery Bradley and Jae Crowder led the Celtics with 21 points each. Isaiah Thomas had 17 points.
Coming off a game seven victory over Washington on Monday night, Boston missed 11 of its first 14 shots.
"They were the better team tonight," Thomas said.
"They hit us first. They were more physical.
"We can't let that happen again."
The Celtics couldn't get anything working when they had the ball, held to just 35 per cent from the field in the first half and 2 for 16 from beyond the arc.
Since Game 5 of last year's NBA finals, Cleveland have won a franchise-record 12 straight playoff games.