LeBron James says he’s not worried after the Cleveland Cavaliers were routed 108-83 Sunday by the Boston Celtics in the opening game of the NBA Eastern Conference final.

But the four-time NBA Most Valuable Player, trying to reach his eighth consecutive NBA Finals, admits the Cavaliers need to make some changes before the best-of-seven playoff series resumes Tuesday in Boston.

“I have zero level of concern at this stage,” James said. “You get better throughout the series. I’ve been down 0-1. I’ve been down 0-2. I’ve been down before. We have another opportunity to be better Tuesday.

“Game one has always been a feel-out game for me. I got a sense of how they are going to play me and I can make some changes going into game two. We’ll see ways we can be better and get our offence into a better rhythm.”

Jaylen Brown scored 23 points and grabbed eight rebounds while Al Horford added 20 points for the Celtics, who seized a 36-18 lead after the first quarter and never looked back, inflicting the second-worst game one playoff loss James has ever suffered.

“We were great,” Horford said. “We came out with a lot of energy. We fed off the crowd and we kept it going throughout the game. We’re just out here playing hard and doing the best we can.”

Marcus Morris had 18 points and 11 rebounds for Boston and led a swarming defensive effort that shut down Cavs playmaker James, who averaged 34 points, 9.4 rebounds and 9.0 assists in prior playoff games.

“We just have to make it hard for him,” Celtics coach Brad Stevens said. “Our guys played with good aggression.”

James finished with 15 points on 5-of-16 shooting with seven rebounds and nine assists. He blocked two shots but also made seven turnovers as the Cavaliers missed their first 14 3-point attempts and came no closer than 14 points in the second half.

“They had a great game plan in game one,” James said. “They did a great job of communicating the whole game. We have a lot of film to look at how they were making us uncomfortable. I was out of my rhythm the whole game.”

Containing LeBron

Morris boasted he was the best defender to guard James and led the hustling work that contained the 33-year-old Cleveland superstar, who has more career playoff appearances than the entire Celtics roster combined.

“It was a team effort,” Morris said. “Everybody played their part in guarding him. We did a great job of that.”

The Celtics forced James to work harder defensively as well.

“They showed two bodies (against James) all night,” Cavaliers coach Tyronn Lue said. “When he thought he had driving lanes, they made him kick it out to other shooters.

“We didn’t play well. We know we have to play better. They attacked us early on. We had some great shots we couldn’t make and it snowballed from there.”

‘Young guys are special’

Kevin Love led Cleveland with 17 points and added eight rebounds. Tristan Thompson had a game-high 11 rebounds off the Cavs’ bench. Jayson Tatum added 16 for Boston and Terry Rozier had eight points and seven assists.

Talented 20-something players Tatum, Rozier and Brown have filled the void left by injured stars Kyrie Irving and Gordon Hayward, combining with Horford – who has been eliminated by James four times in the playoffs – to out-hustle and dominate.

“Our young guys are special. They have been showing it all year,” Morris said. “Their mentality, the way they carry themselves, is like veterans in this league. It’s very unfortunate we had those injuries but no one is going to feel sorry for us. Other guys got the opportunity. We’ve had to step up.”

Boston surged ahead 61-35, the biggest half-time playoff deficit of James’s career. Cleveland pulled within 78-64 entering the fourth quarter, but Boston answered with an 18-4 spurt that sealed Cleveland’s fate.

“We’ve got a lot of room to improve,” Stevens said. “We got stagnant in their third quarter run. We’re very aware we will get a heavyweight punch Tuesday.”