Dallas guard Jason Terry and Dirk Nowitzki (41) celebrate after Terry hit a three-pointer in the closing seconds of Game 5 of the NBA finals. The Mavs took a 3-2 series lead with a 112-103 win on Thursday in Dallas.

Dallas ? Dirk Nowitzki thrust both arms in the air, a sea of blue screaming around him and the Dallas Mavericks finally ahead in these ultra-close NBA finals.

Now it really is “now or never” for LeBron James and the Miami Heat.

Nowitzki scored 29 points, driving for the go-ahead dunk with 2:45 remaining, and the Mavericks beat the Heat, 112-103, on Thursday night to take a 3-2 lead in the NBA finals.

Five years after going up 2-0 on the Heat, the Mavs finally got that elusive third victory, and can wrap up their first championship in Game 6 at Miami on Sunday night.

“We’re a very resilient team, you know that,” guard Jason Terry said. “We’ve been in tough battles all playoffs long. It’s not going to stop. It’s going to get even harder. But we’re ready. We’re determined, and this is our time.”

James, who called this game “now or never,” responded from his worst playoff performance with 17 points, 10 rebounds and 10 assists, and Dwyane Wade battled through a sore left hip after a first-quarter collision to finish with 23 points.

Chris Bosh had 19 points and 10 rebounds for the Heat, who get the final two games at home with history against them as they try to win a title in their first season together: In the 26 previous finals that were tied 2-2, the Game 5 winner won 19 of them.

“We fought hard all season for home-court advantage. We’re down 3-2,” Bosh said. “We protect home court, we win the series, so we just have to keep that in mind.”

The Mavs shot 60 percent through three quarters, briefly gave up the lead in the fourth, then controlled the final few minutes, just as they had in thrilling comebacks in Games 2 and 4.

This time, they got to play from ahead thanks to some sizzling shooting: 56.5 percent from the field, including 13 of 19 (68 percent) from three-point range.

“We made more shots,” Dallas coach Rick Carlisle said. “We did a lot of good things defensively, which led to good offense. … You never know when the games are going to go that way. The thing we’ve got to do is we’ve got to make sure our defense is consistent.”

Terry scored 21 points and J.J. Barea had 17 for the Mavs, who insisted at some point their shots would start falling even against the Heat’s stingy defense. Jason Kidd and Tyson Chandler both finished with 13 points.

“I felt great. I was in rhythm tonight,” Terry said.