OKLAHOMA CITY -- With about five minutes to go in the Sunday game against the Oklahoma City Thunder, Dallas Mavericks rookie point guard Dennis Smith Jr. reached a realization after a slow start.

These situations -- tight games in the fourth quarter -- were where he needed to come through.

Smith was quiet for much of the game as the Thunder put him under extreme pressure. However, he finished big, scoring 11 points in the final 1:39 to lift Dallas to a 116-113 win at Chesapeake Energy Arena.

"It was time for me to get it going," Smith said.

Smith's growth has been a continuing storyline for the Mavericks (13-25) throughout their current four-game winning streak, especially over the past two.

He didn't get close to a triple-double after a game after becoming the third-youngest player in league history to accomplish that statistical feat, but Smith lifted his team at the end.

Smith finished with 19 points, four rebounds and six assists.

"He was great tonight," Mavericks coach Rick Carlisle said. "It was an up-and-down night, there was a lot going on. They were trapping him in the pick-and-rolls. He hasn't seen that. He went through some situations that were very difficult, but he kept his energy up, he kept his head up, he kept attacking."

Just so much growth.

And Smith did it against one of the league's preeminent point guards.

Oklahoma City's Russell Westbrook turned in another huge night -- 38 points, 15 rebounds and 11 assists -- but couldn't match Smith in the end as the Thunder dropped their second consecutive game.

In the final two minutes, the point guards took over.

Moments after Jerami Grant put the Thunder ahead with 1:52 remaining, Smith calmly sank a 3-pointer to put the Mavericks ahead 108-106.

Westbrook responded with a layup to tie it before Smith hit another 3-pointer.

In the final minute, with Dallas holding a one-point lead, Smith drove hard to the rim and finished with a layup to extend the margin.

Smith added a pair of free throws, but it was a missed free throw that gave the Thunder hope.

Westbrook grabbed the rebound off the miss and barreled up the court with a head of steam. Westbrook's 3-point try clanged off the rim, but the ball bounced out of bounds off a Mavericks player to give Oklahoma City one more chance with 3.6 seconds to play.

Westbrook's ensuing 3-point attempt missed the mark, too, dropping the Thunder to 20-17.

"We just didn't get the stops we needed to," Westbrook said.

Up until the final flurry, Westbrook had been excellent in the fourth quarter, going 7 of 9 from the floor, all from inside the arc, before missing the first of three 3-pointers with 20.9 seconds left.

Harrison Barnes led the Mavericks with 24 points in what Carlisle called the best game of his season. Barnes was 10 of 15 from the floor and 4 of 6 from behind the 3-point arc. Dirk Nowitzki scored 13, and J.J. Barea added 12 points and 11 assists for Dallas.

Paul George scored 25 for the Thunder (20-17), and Carmelo Anthony added 21.

The Mavericks shot 51.7 percent from the floor overall. They scored 35 first-quarter points and 32 in the final quarter.

"We're going to need to get back to our identity, which has been really an elite defensive team for really most of the year," Thunder coach Billy Donovan said. "You can see as games have gone here the last week or so, there's been slippage, and we've got to get back to that.

"We're doing some good things on offense, but I feel like defensively, we've got to get back to that being our staple and continue to grow offensively."

NOTES: The Thunder's Josh Huestis made his first career start, playing at guard with Andre Roberson out with left patellar tendinitis. Huestis was scoreless and grabbed six rebounds in 19 minutes. ... Mavericks PF Josh McRoberts was active for the first time this season as he progresses from a series of injuries that have kept him out after joining Dallas in the offseason. McRoberts did not play. ... Thunder PF Patrick Patterson was fined $10,000 for a tweet criticizing officials following Oklahoma City's Friday loss to Milwaukee. Patterson's tweet came in response to the NBA's report that the Bucks' Giannis Antetokounmpo stepped out of bounds just before slamming home his game-winning dunk. ... Dallas outshot Oklahoma City 51.7 percent to 48.3 percent to improve to 12-3 this season when outshooting its opponent.