Replays showed he released the shot with one-tenth of a second left on the clock.
Still working his way back into shape, Nowitzki proved to be a liability during Oklahoma City's 17-6 fourth-quarter comeback. He sagged off of Durant far enough that the three-time NBA scoring champion could drill a 3-pointer from the left wing, then was trailing a play when O.J. Mayo backed into him and lost the ball to set up Durant's fast-break dunk and three-point play.
Durant's right-handed hook shot from the right block gave Oklahoma City its first lead since the opening 4 minutes at 96-95 with 1:57 to play.
Oklahoma City came up empty on three chances to extend the lead — after back-to-back offensive rebounds by Ibaka — but Durant hit a pair of free throws with 3.7 seconds left after Westbrook stole the ball from Mayo and dove to cover it while calling timeout.
In overtime, Carlisle pulled Nowitzki in favor of Marion for defense at one point.
Kaman ended up with 17 poitns and Marion chipped in 14 points and nine rebounds for the Mavericks, who were swept on a treacherous three-game road trip that featured stops at West contenders Memphis, San Antonio and Oklahoma City despite getting Nowitzki back. Dallas has lost seven of eight.
Dallas had been 11-1 this season when leading at the beginning of the fourth quarter and 11-2 after holding a 10-point lead or larger. Mayo, who had been averaging 20.6 points, scored only four and has 29 total over the last four games.
Oklahoma City had won 12 in a row before losing back-to-back games at Minnesota and Miami.
The franchises have grown quite familiar over the past two seasons, with each team taking a turn knocking the other out of the playoffs — in addition to their proximity along Interstate 35 and a handful of preseason matchups to go with the usual regular-season meetings. Dallas eliminated Oklahoma City in the Western Conference finals before winning the NBA title in 2011 and the Thunder swept the Mavs in the first round last season.