Oklahoma City ? Trailing by 15 points with only 5 minutes to play in one of the NBA’s rowdiest arenas, the Dallas Mavericks were just wishing and hoping for the best.

Dirk Nowitzki and Jason Kidd delivered, and the Mavs suddenly find themselves only one win away from the NBA finals.

Nowitzki scored 40 points, Kidd hit the go-ahead three-pointer with 40 seconds left in overtime, and the Mavericks staged an improbable rally to stun the Oklahoma City Thunder, 112-105, on Monday night and take a 3-1 lead in the Western Conference finals.

“You’re lying if you’re not surprised. Down 15 with five minutes to play you’re thinking hopefully something can happen,” Dallas center Brendan Haywood said. “You’re just kind of wishing.”

Dallas didn’t lead until Nowitzki hit two free throws 16 seconds into overtime, needing to rally from a 99-84 deficit in the final five minutes of regulation. The Mavericks never let the Thunder — who were one win shy of tying an NBA record with eight OT wins in the regular season — go ahead in the extra period.

“There’s times and situations where they are going to test the courage and the mental inner strength of your team,” said Jason Terry, who scored 20 for Dallas. “This was one of those times.

“This was a defining moment in our season where we look back and say, ‘Hey, that was the game”‘

Kevin Durant missed a three-pointer on Oklahoma City’s opening possession of overtime then didn’t get another shot until he missed a three off the front rim in the final 10 seconds with the Thunder down by five.

Durant finished with 29 points and 15 rebounds, and Serge Ibaka had 18 points and 10 boards for Oklahoma City. Russell Westbrook added 19 points, eight rebounds and eight assists.

The Thunder suffered their first consecutive losses of the postseason and first back-to-back home losses in six months.

Only two teams have come back from 3-1 deficits in NBA history without the benefit of home-court advantage in Game 7 — Houston in the 1995 West semifinals and Boston in the 1968 East finals.

“There’s no doubt it was a tough loss,” Oklahoma City coach Scott Brooks said. “If this loss did not hurt, there’s no such thing as a loss that can hurt you.”

Game 5 is Wednesday night in Dallas.

“We worked really hard these two games to win, and none of that guarantees anything for Game 5. We know that,” said coach Rick Carlisle, whose Mavs have won at least 50 games in 11 straight seasons with no titles and only one trip to the NBA finals to show for it.

“All of us involved with this team have been through a lot of these wars. We understand our position that we’re in. We respect it. We’re very humble about it. We’ve got to get ourselves revved up and ready for Wednesday, because that’s an opportunity.”

Durant had nine of the Thunder’s 26 turnovers, including the one that led to the big shot by the 38-year-old Kidd.

Kidd stripped him as he went up for a shot with just over a minute left in overtime, then took a pass from Nowitzki, pump-faked to get Westbrook in the air and stepped up to drill a three-pointer to put Dallas up 108-105 with 40.3 seconds left.

Kidd scored 17 to go with seven assists, five rebounds and four steals.

“Everybody asks questions about the age and all that other stuff,” Carlisle said, “but the thing I’d say to anybody is, ‘Never underestimate greatness.”‘

Westbrook missed on a drive on Oklahoma City’s next possession, and Terry hit two free throws with 13 seconds left to give the Mavs a two-possession lead. Durant finally got another shot off, squatting with his head hanging down as Kidd walked up for two free throws to provide the final margin.

“We kept believing,” Nowitzki said. “I think finally we got some rebounds. I think that was killing us all night long.”