Rajon Rondo played with one arm, Shaquille O’Neal actually played basketball and Kevin Garnett submitted a vintage performance — and it all added up to a gritty 97-81 Celtics victory in what was essentially a must-win Game 3 against the Heat in the Eastern Conference semifinals.

In a scary third-quarter moment, Rondo got tangled up with Dwyane Wade and dislocated his elbow. After receiving treatment, he shockingly returned for the fourth quarter — finishing with 11 assists and six points with essentially one arm. Meanwhile, Shaq scored just two points in eight minutes.

If not for those two Celtics comebacks, Garnett would’ve been the headliner — totaling 28 points and 18 rebounds in the victory. Wade led the Heat with 23 points, and Mario Chalmers added 17 off the bench.

WHAT WENT RIGHT

The Big Three: Even before Rondo went to the locker room with an elbow injury — and especially while Rondo got treatment — the Celtics’ Big Three asserted themselves and carried the team on both ends of the floor. The trio looked as sharp as they had all series, totaling 70 points on 26-of-51 shooting. Paul Pierce nearly matched Garnett’s output with 27 points of his own.

Meanwhile, the C’s Big Three held Wade, LeBron James and Chris Bosh to 43 combined points on 15-of-41 shooting. Bosh was nearly invisible, totaling only six points and five rebounds.

Encouraging start: For the first 5:07 of Game 3, the Celtics appeared ready to seize early control and set a tone for what the Heat could expect in Boston. The Garden crowd was loud, and the starting five’s play spoke louder. Behind a stifling defense and out of the flow of a well executed offense, Pierce scored 10 early points as the Celtics took a 16-7 lead — forcing Heat coach Erik Spoelstra to spend a timeout with 6:53 still remaining in the first quarter.

Shaq comes back: With 2:41 remaining in the first quarter, Shaq returned to the court for the first time this postseason and just the second time since Feb. 1. A minute and a half later, he scored his first bucket to put the Celtics up 27-20.  He played 4:46 in the first half — lumbering for much of it, but also altering at least a few Miami shots on the defensive end. His final line of two points and one rebound were less climactic — but his 8:29 playing time was certainly encouraging.

WHAT WENT WRONG

Down goes Rajon Rondo: With 7:01 left in the third quarter, Wade and Rondo got tied up in the paint on the Celtics end, and Rondo landed awkwardly on his arm — appearing to hyperextend his left elbow. After clutching his arm on the floor for what seemed like an eternity, trainer Ed Lacerte ushered Rondo — and what appeared to be the C’s season — into the locker room.

At the end of the third quarter, Rondo returned to the Celtics bench with a dislocated elbow. And he returned to the floor to start the fourth quarter, bringing the crowd to a deafening level. He played the entire fourth quarter.

Joel Anthony’s energy: As has been the case all series long, the Celtics had no answer for Anthony (12 points, 11 rebounds) off the bench. He recorded 10 points (on 5-of-5 shooting) and seven rebounds in the first half alone. Four of those seven boards came on the offensive end, where he often found himself wide open underneath the basket (hence the perfect first-half field-goal percentage).

Ray Allen’s foul trouble: Questionable or not, Allen picked up his third foul with 6:48 still to play in the second quarter as he brushed Wade’s elbow on a 3-point attempt. The whistle came on the heels of a string of questionable calls by the refereeing crew of Bob Delaney, Bill Kennedy and Steve Javie. Also, Moments after Rondo’s injury, Wade took down Allen underneath the basket, and Allen had to be restrained from going after Wade — a rare but understandable burst of anger for the 3-point king, for certain.