James can answer his critics by leading the Heat to a win tonight. (Getty Images)

BOSTON -- Now is the time for LeBron James. This is the moment.

This is the latest moment when everything he has invested in this chase for that elusive first championship collides with all the forces conspiring to stop him.

Including forces from within.

LeBron vs. the Celtics. LeBron vs. the critics.

LeBron vs. LeBron.

This is it.

Facing yet another monumental challenge in Boston against the Celtics, with the crushing reality of playoff elimination at hand, we find out what James is made of Thursday night at TD Garden.

For the sake of the Heat, and the current, tenuous state of LeBron's legacy, James had better be made of something different than what was exposed to the world in Game 5.

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James has faced these moments before. He's faced playoff elimination in Boston twice before, losing both times -- both with Cleveland, in 2008 and and 2010, both in the conference semifinals. The most crushing defeat, and the one that prompted him to leave the Cavs and form his own superteam in Miami to counter the Celtics' Big Three, came in 2010. Following a 3-for-14 performance at home in Game 5 in which James was oddly disengaged, he had 27 points and 19 rebounds as the Celtics ousted him from the postseason for the second time in three years.

That scenario is the one that applies most appropriately to Game 6 in Boston Thursday night, because James once again was a bystander in the clutch moments when Game 5 was decided in Miami Tuesday night.

In the final 7 1-2 minutes during which the Heat fluctuated between a six-point lead and a four-point deficit and ultimately went down in flames, James attempted just four shots. On three straight possessions, James literally stood in the corner or on the baseline and barely moved. It's one thing to defer to Dwyane Wade down the stretch; it's quite another to literally just stand there and do nothing.

Was it exhaustion? Exhaustion, for one of the most finely tuned athletic specimens ever to suit up in professional sports? Wade, for one, wasn't buying it.

"I'm sure he was a little tired," Wade said. "A lot of guys out there are tired. LeBron is one of the best conditioned athletes in our game, so I never worry about him."

With the Heat's season and his own reputation on the line, here's how James' final 6:17 went in Game 5, courtesy of video clips on NBA.com/stats, the league's media website:

* 6:17: Wade makes a driving layup that gives Miami a 78-72 lead. LeBron spends the entire possession on the baseline with his hands on his knees, at one point directing traffic but never moving.

* 5:29: James Jones misses a 3-pointer with Miami leading 78-75. LeBron spends half the possession in the right corner with his hands on his knees, then motions angrily for Mario Chalmers to switch sides of the floor before spending the rest of the possession standing in the corner.

* 5:02: Wade misses a 20-footer. LeBron starts out in the right corner again, creeps to the right wing outside the 3-point line, gets a pass from Wade and sends it right back before Wade misses the jumper. Miami still leads 78-75

* 4:29: Wade makes a 20-footer. James hangs out on the perimeter, playing catch with Wade. Miami leads 80-77.

* 3:50: Wade misses a driving layup after playing catch with LeBron, who starts on the perimeter, gives it back to Wade and runs through the lane to the other side of the floor, where he's no threat. Miami leads 80-79.

* 3:19: LeBron has a driving layup attempt blocked by Kevin Garnett. After getting a defensive rebound, James initiates the offense, directing traffic and maneuvering around a screen from Udonis Haslem before driving unsuccessfully on Garnett. It's his first field-goal attempt in more than four minutes.

* 2:34: Chalmers makes a 3-pointer to give Miami an 83-82 lead. James drives the lane on Ray Allen, passes to Battier in the corner, who passes to Chalmers. A good play with a good result.

* 1:39: Wade makes a driving layup to tie it at 85-85. James forces Mickael Pietrus to switch onto him, and Wade drives into James' area of the floor and converts a tough look in traffic -- despite James and the defender guarding him being in the way.

* 1:13: LeBron misses a contested, catch-and-shoot 3-pointer from the left side. Boston leads 87-85.

* 0:45: With Miami trailing 90-86 after Pietrus' 3-pointer, James drives baseline left, passes to Battier at the top, who passes to Chalmers for a missed 3-point attempt. Same decision as the one with 2:34 left, only with a different result. Boston ball.

* 0:09: James takes the inbounds at the top and drives for a layup to cut it to 92-90. But it's too late. Boston is on its way to the first road win in this series, and a stunning one at that.

Stunning because nobody -- apparently, least of all LeBron -- thought the Celtics had this in them. 

Now, we await James' response. Surely, he has more to offer than he did in the final 7 1-2 minutes of Game 5. Surely, he will play with a fury and aggressiveness that few humans possess the ability to display.

He'll do that, right?

Right?