Rajon Rondo is the best player in this series, better than LeBron “Bury my Game at Wounded Wing” James. But the skinny Boston point guard isn’t the reason the Celtics are on the verge of closing another chapter in the long and miserable history of Cleveland sports.

It’s never one player, as the Cavs should be able to tell you by now. They have the best player in the game, the reigning two-time MVP, and all it’s gotten them is a 3-2 deficit with Game 6 in the hostile confines of TD Garden.

It could be the last game Cleveland plays this year. More important, it could be the last game LeBron plays in a Cavs’ uniform. After looking around at the help he didn’t get and the likelihood that his supporting cast isn’t going to get better, it’s quite likely LeBron will leave town as a free agent.

If so, he goes as the most exciting player in any sport Cleveland has had since Jim Brown. But Brown won a title. LeBron hasn’t.

The only thing that would keep him in Cleveland would be winning the NBA championship. But he’s not playing as if that’s all that important. Tuesday night, he looked lost, as if he’d met his teammates in the locker room five minutes before the game.

This is not good for Cleveland. The only way the Cavs can beat Boston is if LeBron puts up two straight 40-point, triple-double performances. He’s not healthy enough and the Celts aren’t accommodating enough for that to happen.

You never say a great player can’t win a game all by himself. LeBron’s done it once in this series, in Game 3. He could do it again.

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But you know that’s a stretch, because LeBron is getting as much support from his teammates as President Obama is from Senate Republicans.

Compare that to Rondo, who was able to take the first half off Tuesday and still watch his team win by 32.

Before Game 5, a lot of people were going to give all the credit for a Celtics win to Rondo. It’s easy to see why. The kid has been a better player over five games than anyone on the court, including LeBron. Before the series began, Boston was about the Big Three. Now, it’s the Big One with three pretty good supporting players.

Rondo is a skinny little squirt, the kind of player you just hated on the playground because guarding him was like guarding the reflection of a shadow. You could see him, but even if you stood in front of him, he seemed to move right through you, except he didn’t move. He flowed.

But as great as Rondo has been, the reason the Celtics annihilated Cleveland in Game 5 on Tuesday wasn’t him. He didn’t score a single point in the first half and didn’t do much else, either. Even handing out an assist seemed a bigger task than backfilling the Grand Canyon with a salad fork.

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Instead, Boston’s Big Three checked back into the game. We’d almost forgotten how good Kevin Garnett, Ray Allen and Paul Pierce are when they’re on their games. Blame Rondo’s brilliance for that.

Tuesday night, we got a demonstration of just what they can do. Allen was deadly from outside. The Cavs could have dropped a piano on him and he still would have drained the shot — and the free throw. Garnett and Pierce were opportunistic and also deadly. Allen finished with 25, Garnett with 18 and Pierce with 21. That’s 64 points right there.

With Rondo contributing nothing, the Celtics took a six-point halftime lead. In the second half, Rondo decided to score. He made it look easier than scratching your nose, and against Cleveland’s defense, it was that easy. With Rondo putting in 16, the Celtics ran away to a 120-88 win. And it wasn’t even that close.

LeBron, meanwhile, couldn’t get going. He shot 3-for-14 and had just 15 points. After ringing up five assists and five rebounds in the first half, he added just two assists and one board in the second. It could be the elbow, or it could just be that he woke up Tuesday morning and realized he’s surrounded by garbage.

Any way you look at it, it was the second worst playoff game of his career, surpassed in ineptitude only by his non-performance in Game 1 of the Cavs’ 2008 playoff series against the Celtics. LeBron was 2-for-18 in that game with 10 turnovers and the Cavs lost the game and went on to lose the series in seven games.

They’re on their way to losing this one in six. LeBron could change that, but no one else on Cleveland’s team has shown capacity or the inclination to help. Antwan Jamison is a great scorer who’s forgotten how. Point guard Mo Williams can light up a scoreboard — in the regular season. In the playoffs, he has been almost as useful as sunscreen in a coal mine. If it hadn’t been for Shaquille O’Neal’s 21 points, the Cavs would have lost by 40.

Great players win championships. So do great teams. In this series, it’s the Celtics with both the great player and the great team. All Cleveland has is one great player who’s not playing great.

And it doesn’t look as if the Cavs will have him much longer. If you were he, would you stay?

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