The pain was so great, LeBron James said, that his body practically shut down on him.

He could hardly stand, certainly couldn’t run. Good thing all he needed to do was shoot.

A limping, grimacing James shook off the pain of left leg cramps to hit a tiebreaking 3-pointer with 2:51 remaining and the Miami Heat held off the Oklahoma City Thunder for a 104-98 victory Tuesday night and a 3-1 lead in the NBA Finals that no team has ever blown.

“He was hurting,” teammate Dwyane Wade said. “But that’s what it’s about this time of the year. It would hurt more if we lose the ballgame, so it feels a little better if you can win it.”

Imagine how good it will feel if the Heat get one more victory.

Better get well fast, LeBron. You’re one win from the biggest party of your life.

Game 5 is Thursday night and James will have a chance to finish a nine-year chase that started in Cleveland before he famously — or infamously — left for South Florida before last season.

With James watching the final moments, Mario Chalmers finished off a stellar 25-point effort that matched Wade. James had 26 points, 12 assists and nine rebounds, missing a shot at a triple-double only because he was on the bench at the end after the thigh cramps emerged following a fall near the Thunder basket.

The Heat needed all James could give and more to hold off Russell Westbrook. He scored 43 points for the Thunder, who wasted an early 17- point lead but were never out of the game because of their sensational point guard. Kevin Durant had 28 points but James Harden threw in another clunker, finishing with eight points on 2-of-10 shooting. Westbrook and Durant were the only Thunder players to score in the last 16:46.

James stumbled to the court on a drive midway through the fourth quarter, staying on the offensive end of the floor as the Heat regained possession on a blocked shot, and he made a short jumper that made it 92- 90. After Westbrook missed a jumper, the Heat called timeout as James gingerly went to the court. Unable to walk off, he was carried to the sideline.

He returned to a huge roar with a little over four minutes left and the Heat down two, and after Chris Bosh tied it, James slowly walked into a pull-up 3-point attempt — perhaps doing so knowing he couldn’t drive by anyone — and drilled it.

That made it 97-94, and when Wade followed with a layup with 2:19 left, the Heat finally had enough room to withstand Westbrook, who kept coming all night.

Chalmers, the player who was struggling so badly that the Thunder put Durant on him in hopes of avoiding further foul trouble, made 9 of 15 shots, scoring more points than he had in the previous three games.

The Heat couldn’t have done it without James, who refused to let any pain prevent him from taking the biggest step of his career.

The Heat led 2-1 in the finals last year but James’ struggles were their biggest problem as they lost the next three to Dallas. He was at his brilliant best in this one, keeping up his scoring surge but also willingly kicking it out to open teammates whenever he was double-teamed.

He tried to play through the pain, but the Heat had to call another timeout and remove him for good shortly after his go-ahead basket, and Spoelstra said the Heat couldn’t keep playing four against five.

Bosh finished with 13 points and nine rebounds for the Heat, who quickly climbed out of the 17-point hole by scoring 16 straight points, with Chalmers and backup Norris Cole helping steady them until James and Wade got going.

In foul trouble the last two games, Durant began the game covering Chalmers, an adjustment that freed him from the burden of defending James. It kept Durant safe from fouls.