DALLAS, March 14 (Ticker) -- The Dallas Mavericks spotted LeBron James and the Cleveland Cavaliers a big lead but weren't about to lose at home to an Eastern Conference opponent.

Dirk Nowitzki shrugged off a slow start to score 30 points and the Mavericks overcame 36 points by James and a 19-point halftime deficit for a 91-87 victory and a perfect home record against the East.

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The victory also allowed the Mavericks (50-14) to join San Antonio as teams that have clinched a spot in the Western Conference playoffs.

While Nowitzki was struggling with 4-of-14 shooting in the opening two quarters, Cleveland raced to a 53-34 lead. The Cavaliers opened things up in the second quarter, when they outscored the Mavericks, 31-15.

James scored 10 points in the period and 18 in the half. Cavaliers center Zydrunas Ilgauskas had 13 points in the first half and ended up with 17.

"LeBron was on a roll and we couldn't stop Ilgauskas," Nowitzki said. "Offensively, we never really got anything going. It was a tough outing early."

Mavericks coach Avery Johnson has been pretty animated at some of his postgame media briefings lately and there is no doubt he got after his team Tuesday. Whatever he said, it worked.

Dallas outscored Cleveland, 27-8, in the third quarter to move into a 61-61 tie. Nowitzki and Marquis Daniels each scored eight points and Jason Terry added seven in the period.

"We talked at the half about being more aggressive," Nowitzki said. "In the third quarter, we hit them (defensively) at halfcourt and really started to pick our energy up more than anything and it really worked well. We finally found a way to stop Ilgauskas a little bit and keep the ball out of his hands. We doubled LeBron when he came off of screens to get the ball out of his hands some."

"Avery challenged me at halftime," Terry said. "He told me to get aggressive. Guys looked for me, I got a couple of open shots and Dirk put us on his back in that run in the third."

Dallas opened the final quarter on a 9-2 run to take the lead for good. Nowitzki scored seven points in the burst, including a 3-pointer that capped it and gave the Mavs a 70-63 lead with 9:42 to play.

"It's hard to contain a player like him the whole game," Ilgauskas said. "Sooner or later, he's going to get rolling. We did a good job on him in the first half. In the second half, he made some shots and his confidence was up and he started rolling."

"The third quarter was a disaster," James said. "We weren't able to counter their attack. They made big shots and we weren't able to make any shots. We knew they would heat up but we didn't counter it."

James scored on a layup to pull Cleveland within 86-84 with 15 seconds left, but Darrell Armstrong hit a pair from the line to push the lead back to four.

On the ensuing possession, Nowitzki challenged James on a drive and Ilgauskas missed three follow shots before Nowitzki finally corralled the rebound. He was fouled and made both free throws to make it 80-84 with six seconds remaining.

Terry scored 20 points and Daniels 17 for Dallas, which went 15-0 at the American Airlines Center against the East this season.

Erick Dampier had seven points, 13 rebounds and two blocks off the bench for Dallas. Nine of his rebounds and two of his blocks came in the second half.

"We made adjustments in the second half and went out there and played the way we are capable of playing," Dampier said. "We just have to start every game like that from the beginning and don't make ourselves have to come from behind."

Ronald Murray added 12 points for Cleveland, which has lost three straight following a four-game winning streak.

"It's two games in a row in playoff teams' building where we had a lead and our opponent just decided, 'Hey, let's turn it up,'" Cavaliers coach Mike Brown said. "They turned it up and we did not respond. We go away from everything that we are taught because they decide to step it up a notch. The crowd is loud and the intensity of the game vs. a playoff team in their building is a lot. Twice, that's been too much for us to handle."

This is the earliest point in a season that any Mavericks team has reached 50 wins.

"We're mentally tough and we're very focused and determined to improve on last season," Terry said. "It also says something about the coaching staff and our system. It says something about our city, our fans. We're just a good ballclub right now from top to bottom."