Udonis Haslem was one of the Miami Heat's NBA Finals heroes in 2006, defending Dirk Nowitzki exceedingly well as the Heat beat the Dallas Mavericks in six to claim their first, and to this point only, NBA title. As such, the Heat are relying heavily on Haslem, one of just two remaining members of the title team (with Dwyane Wade), to give Miami solid minutes off the bench in the 2011 championship series against scorching Dirk and the Mavs. In Game 1, Haslem did his job.
Nowitzki was held to 27 points on 7-18 shooting with 12 free throws in Game 1. Saying a player was held to 27 points seems funny, but Dirk struggled; he was 5-14 with 17 points entering the fourth quarter. Haslem played 30 minutes overall, and 23.5 minutes with Nowitzki on the floor. Haslem was the primary defender on Nowitzki throughout those minutes, though Miami sent plenty of help once Dirk touched the ball.
With Haslem on the floor, Nowitzki scored 19 points on 4-7 shooting from the floor and 10-10 shooting from the line. He also had two turnovers. In the 16 minutes Dirk played while being defended by Chris Bosh or Joel Anthony, Nowitzki scored eight points on 3-11 shooting with two free throws and zero turnovers.
While that looks like Bosh and Anthony did a better job on Nowitzki, keep in mind that Dirk missed plenty of shots he'd normally make, including a plethora of gimmes at the rim. Haslem's great success in guarding Nowitzki comes from denying the ball; that's all about working hard before the pass comes, to recover off of screens and misdirection.
To wit, Dirk has 12 shot attempts in 23.5 minutes against Haslem (about one every two minutes) and 12 in 16 minutes (one every 80 seconds) against Anthony and Bosh. If you assume Dirk will hit a greater share of his shots going forward, you want the guy who can limit those touches in the game. Haslem indicated he's that guy in Game 1.