With Orlando leading a series that most thought they would be beaten, and playing at home, this is a huge game in the series.
A win all but condemns Cleveland to an exit, whereas a win puts them back in the driver's seat.
The key for Cleveland will be stopping the Magic's dominant frontcourt from taking over the game—leaving LeBron with a one-man, uphill battle.
Interestingly, the Cavs have opted to use LeBron to defend what is probably Orlando's weakest scoring option in the starting lineup—Rafer Alston (which says something of the depth of scoring ability that the Magic possess).
A similar ploy was used by the Lakers against the Celtics in last years finals. Kobe played a "sagging" defense on Rondo, taking away Rondo's only method of scoring (driving to the basket) and kept Kobe fresh on the offensive end.
This tactic doesn't work anywhere near as well in this matchup.
The first reason for this is the fact that Alston has a legitimate jumpshot. Rondo had nothing of the sort. LeBron also doesn't have the short-distance quickness that Kobe has (he's really too big to have that kind of quickness). And we've seen the result, which is Alston finding ways around LeBron much easier than he would West or Williams.
So in essence, the Cavs have taken one of the league's best one-on-one defenders and turned him into a defensive liability.
The other reason that it doesn't work for the Cavs is the fact that none of the Celtics' other players were genuine matchup nightmares. Paul Pierce, Ray Allen and Kevin Garnett are just great players. They're too prototypical for their positions to be considered matchup nightmares.
Orlando have two guys that create such issues—Rashard Lewis and Hedo Turkoglu. Rashard is basically Dirk Nowitzki with a post game. If he was given the keys to a team (which he never has, playing in the shadows of Ray Allen and Dwight Howard), he'd be considered one of the league's best.
Then you've got Turkoglu, who has the the length of a PF, the shooting range of a two-guard and the distribution skills of a point guard. He can cause the Cavs problems, even when his shots aren't falling—as evidenced by his 13-point, 10-rebound, seven-assist night, where he shot just 1-11 from the field.
If the Cavs want to slow these two down, they need to put LeBron on one of them. It'll tire him out—and while he might not be putting up 40 points a night, it gives the Cavs a much better shot at winning the basketball game.