Rajon Rondo reentered TD Garden in the third quarter wearing warm-ups.  He walked without the aid of crutches; only a slight limp hinted at why he was not on the floor.

An MRI on his right knee at New England Baptist revealed a torn ACL.  Rondo, a late scratch for the Celtics against the Miami Heat on Sunday, will have surgery to repair the knee he hyperextended in a double-overtime loss to the Atlanta Hawks Friday night.  He is expected to miss the rest of the season.

Rondo changed clothes and took a seat behind the Celtics bench to watch his team earn an unlikely 100-98 double-overtime win against the defending NBA champions in Boston.  The win lifted the Celtics to 21-23 and ended a six-game losing streak.

Courtney Lee started in Rondo’s place, but Paul Pierce inherited Rondo’s role in the Celtics offense.  Pierce finished with 17 points, 13 rebounds and 10 assists, including a jump shot over LeBron James with 30.4 seconds left that put the Celtics ahead for good.  Off a Dwyane Wade miss, Pierce took a pass, hesitated at the three-point line then pushed his way to within 20 feet.  He rose over James outside the right elbow and sank what ended up being the winning field goal.

James missed a shot over Jeff Green at the other end.  Pierce took the rebound out of the air and was fouled as he hit the ground.  He made one of his two free throws, extending the lead to 100-98 but giving the Heat a chance to tie or win.  The Celtic defense was able to force a desperate three-point shot from Shane Battier that didn’t even make it to the rim.  Pierce pressured the shot.

James finished with 34 points, 16 rebounds and seven assists in 52 minutes.  Kevin Garnett led all Celtics with 24 points.

With Rondo absent, the Celtics often ran their offense through Pierce and Garnett.   The two teamed up at the top of the key, with Garnett screening Pierce’s defender then looking for a pass.  Pierce would pass his way out of double-teams, finding an open Garnett.

Despite missing their best passer and the captain of their fast break, the Celtics finished with 24 assists and outscored the Heat 16-8 on fast break points.  The defense forced 20 turnovers, many of them coming off deflected interior passes.  The defense of Jared Sullinger, who started in place of Brandon Bass, helped cool off a hot start from Chris Bosh.  The impossible task of guarding James fell to Jeff Green, but he played solid defense in the overtime periods.  James made only three shots in 10 minutes of extra time.

Ray Allen played well in his first game back in Boston as a member of the Heat.  A video montage welcoming him back was met with a mix of cheers and boos, but  TD Garden fell silent after he hit a corner three-point shot with 25 seconds left in the fourth quarter to help force overtime.  Allen finished with 21 points.

The Celtics move forward without Rondo against the Sacramento Kings at home on Wednesday.  Losing their most talented young player seems disastrous, but the Celtics showed they could do more than tread water without him.  If the defense continues to play well, the Celtics are still dangerous.