CLEVELAND – The window hasn’t closed on the Boston Celtics. It’s still wide open.

Rajon Rondo tied a team playoff record with 19 assists, Ray Allen scored 22 points and the Celtics, showing they’re still very dangerous despite their years, opened a 25-point lead in the fourth and survived Cleveland’s comeback for a 104-86 win on Monday night to even their Eastern Conference semifinal series at 1-1.

After blowing an 11-point lead in the third quarter of Game 1, the Celtics almost squandered a much bigger one. They led 91-66 with 9:08 left, but the Cavs scored 15 straight and pulled within 93-83 on LeBron James’ basket with 3:13 left.

Boston, though, closed with an 11-3 spurt.

James scored 24 and Antawn Jamison had 16 for Cleveland, which was outscored 31-12 in the third.

Game 3 is Friday night in Boston.

The Celtics seemed in control with their 25-point bulge, but they got complacent and found themselves having to scramble down the stretch when they could have been resting.

“We were playing the clock instead of the game and got stagnant,” Rondo said.

But leading 93-83, Boston regrouped. Rondo and Allen scored, then Kevin Garnett completed a three-point play to make it 100-84, allowing Celtics Coach Doc Rivers to finally relax after watching his club play inspired ball most of the way.

Garnett finished with 18 points and 10 rebounds, and Paul Pierce scored 14.

Rasheed Wallace, called out by Rivers after a lousy series opener, added 17 points off the bench as the Celtics stripped the Cavaliers of home-court advantage and gave them four days to think about went wrong.

Two years removed from their 17th NBA title, the Celtics were given little chance of getting past James and the top-seeded Cavs. Despite beating Miami in the first round, Boston was thought to be too old, too slow and too reliant on the aging Big Three of Allen, Garnett and Pierce.

But the trio combined for 54 points, and Rondo, the Celtics’ jitterbugging point guard, set them up with passes from impossible angles. Rondo matched the club’s postseason record for assists set by Hall of Famer Bob Cousy.

Up by four at halftime, the Celtics wasted no time pushing their lead to double digits in the third.

Pierce and Allen hit 3-pointers, and with James tentative — perhaps because of an injured right elbow — and the Cavaliers unable to get anything going on offense or contain Rondo, the Celtics’ lead ballooned to 74-57 on Kendrick Perkins’ basket underneath.

At that point, Cavaliers forward Anderson Varejao showed his frustration by blatantly slamming into Allen on a baseline drive. Allen was sent sprawling and Varejao was assessed a flagrant foul. Allen split the free throws, but on Boston’s next trip he drained a 3-pointer from deep in the corner to make it 78-57.

Anthony Parker threw up his hands in disgust as the Cavs were unable to stop the Celtics’ surge.

James finally shifted into attack mode in the fourth quarter, and Cleveland held Boston without a field goal for 5:39 as the Cavs crept back into it.

But Pierce’s basket with 3:29 left ended the Celtics’ long dry spell, and Boston managed to do enough to prevent a historic meltdown.

Boston’s bench scored just 12 points in Game 1, but Wallace topped that by himself in Game 2. He made his first five shots — three of them 3-pointers — as the Celtics opened a 13-point lead early in the second.