0319 GMT January 23, 2019
The 33-year-old James played all 48 minutes and finished with 35 points, 15 rebounds and nine assists for the Cavaliers who are in the league championship for the fourth consecutive year, AFP reported.
"This is the last chapter for our team this season," said James.
"It's been a whirlwind. It has been roses. There have been thorns in the roses. This is one of the most challenging seasons I have had."
Cleveland became the first team to win on the road in the best-of-seven Eastern Conference championship series and the first to beat the Celtics at home in the postseason.
"Win, loss or draw, at the end of my career you are never going to get someone to say I didn't leave it out on the floor," the four-time league MVP James said.
"We have an opportunity to win a championship. No matter whether we are picked to win or not, we have a great game plan. We are going to try to get better throughout the series," he said.
James led the Cavaliers in the first half with 17 points and 10 rebounds but they trailed for much of the half in front of a crowd of 18,600 at the Boston Garden.
It wasn't until the second half that his supporting cast came to life and the Cavaliers were able to wrestle control back from the Celtics in the low-scoring contest.
"He's unbelievable," said Celtics coach Brad Stevens. "I thought it was an outstanding defensive game. And again he still had 35, 15 and nine. It's ridiculous and he does it with the pressure and scrutiny."
James said he knew ahead of time he was going to have to play 48 minutes.
"It was asked of me tonight to play the whole game, and I just tried to figure out how I could get through it," said James, who played 48 minutes for the first time in a playoff game since 2006 as a 21-year-old against the Detroit Pistons.
"Throughout the timeouts, I was able to catch my breath. At halftime, I didn't come out and warm up. That was my time to recalibrate and catch my wind again.
"I'm the leader of this team, and I'm going to give what I've got."
James said halfway through the season he made up his mind that no matter what happened, he was going to try to keep a positive attitude.
"Right before the break I kind of reset. I didn't know if we were going to make trades or not," he said.
"But I just reset my mindset and said 'OK, this is the season and let's try to make the most of it'."
Jeff Green finished with 19 points and eight rebounds, J.R. Smith tallied 12 points and Tristan Thompson scored 10 for Cleveland, who beat Boston 109-99 on Friday to force Game Seven.
Jayson Tatum paced the Celtic attack with 24 points as Boston suffered their only loss in 11 playoff home games.
Al Horford finished with 17 points and Jaylen Brown had 13 but he was just three-of-12 from the three-point line.