Cleveland is hoping for one more chance.
Kevin Garnett had 26 points and 16 rebounds, and Rajon Rondo added 20 points and 13 assists as the Celtics beat the Cavaliers, 96-89, on Wednesday night to move within a win of the Eastern Conference finals with a 3-2 lead in the best-of-seven series.
Boston is undefeated at home but they have yet to win on the road in these playoffs.
Game 6 is Friday at Cleveland.
"We know it's a win-or-go-home situation. We've got to approach it that way," said LeBron James, who scored 23 of his 35 points in the first 20 minutes and then went cold again. "We're a very good team at home. But a LeBron James team is never desperate."
Paul Pierce scored 29 points and helped shut James down for much of the second half. The Cavaliers forward had 23 points with 3:50 left in the first half but made only one basket in the next 20 minutes as Boston erased a 14-point deficit and took the lead for good.
James, who shot under 26% in the first four games, was 12 of 25 from the field but made only four of his last 14 shots and missed all five of his three-point attempts.
"Whether we get 35 or 20 [from James], it doesn't matter at this point," Cavaliers Coach Mike Brown said. "To lose the game . . . that's what's more disappointing than anything else. Whether he gets this or that, I'm not really concerned, because he's going to contribute in other ways."
Cleveland cut an 88-77 lead to 91-87 on two free throws by Delonte West with 46 seconds left. But, after running down the shot clock, Garnett got the rebound of his own miss and Pierce made five free throws in the last 16 seconds to ice it.
"This momentum, and what we did here tonight," said Garnett, "we've got to figure a way to carry this on the road."