Ray Allen scored 25 points and Rajon Rondo scored all of his 16 in the second half as Boston, considered too old to challenge for another title, proved far too good for LeBron James and Cleveland.
Paul Pierce added 21 and Kevin Garnett 18 for the Celtics, who handed the Cavs their worst home playoff loss in history and can end Cleveland's season with a win in Game 6 on Thursday.
“We cannot come back here,” Garnett said. “We have to think this is our Game 7 coming up and we cannot afford to have the best team in the league have a Game 7 on their floor. Just not possible.” James, the league's two-time MVP on the verge of an expected trip into free agency on July 1, had an atrocious game. He scored 15 points on 3-of-14 shooting, a startling outing for the 25-year-old who has been playing with a sprained elbow.
Because of James' uncertain future, Game 5 may have been his last at home for Cleveland and it has set up Game 6 as the most important in franchise history: Win and force Game 7 on Sunday in Cleveland; lose and maybe watch James, the local kid trying to deliver this city its first pro championship since 1964, leave for good.
Rondo, coming off a 29-point, 18-rebound, 13-assist performance in Game 4, was held without a point in the first half as the Cavs concentrated their defense on stopping the point guard from penetrating into the paint.
He finally got loose in the third, scoring 12 as the Celtics opened a 21-point lead.
Boston went up by 24 in the fourth, sending battered Cleveland fans toward the exits.
James finally checked out with 3:58 and the Celtics leading by 27. He shrugged his shoulders and slapped hands with Cleveland's coaches and teammate Shaquille O'Neal, who had 21 points.
Before the game, Celtics coach Doc Rivers said his team would not change its strategy.
“We don't need anyone to play hero basketball,” Rivers said. “We have to be a team. We're good when we're a team.” And through five games, the Celtics have been the better one. Because of injuries, Boston, two years removed from its 17th NBA championship, has rediscovered its groove after a mediocre regular season.
They've outperformed the top-seeded Cavs in almost every aspect of the game, outrunning and outhustling a younger team that with the addition of O'Neal, Antawn Jamison and Anthony Parker, was built for the postseason but has yet to show it's serious about winning a title.
