DALLAS (AP) -The Oklahoma City Thunder have transformed from doormat to dangerous playoff team.

Kevin Durant scored 23 points, Jeff Green added 22 and the Thunder clinched a playoff spot with a 121-116 victory over the Dallas Mavericks on Saturday night.

Russell Westbrook and Nick Collison added 17 points each to help the Thunder end a nine-game road losing streak against the Mavericks dating to when the team was based in Seattle.

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Oklahoma City missed the playoffs last season after relocating from Seattle. The Thunder are the NBA's most improved team this season, more than doubling their 23 victories in 2008-09.

``It's a great feeling, but I've been impressed with our guys' work ethic all year long and I know that's not going to change,' coach Scott Brooks said.

The Thunder's young players didn't do any postgame celebrating. Their explanation? They have a home game Sunday against Minnesota, which has the worst record in the Western Conference.

``It's cool to celebrate after the game but we've got a quick turnaround ... so we've got to come out there and produce,' Durant said. ``Maybe on our day off we'll celebrate.'

Durant led the way on both ends of the floor, matching a career high with five steals and chipping in five rebounds and five assists.

Dirk Nowitzki had 30 points and 13 rebounds for Dallas, and Jason Kidd added 24 points in the matchup of possible playoff opponents.

``They play hard,' said Dallas' Jason Terry, who went 2 for 10 from the field, 0 for 6 from 3-point range, and finished with four points. ``We might see them again in the playoffs. Who knows?'

The Mavericks are 5-6 since ending a season-best 13-game winning streak, a slump that has been rooted on the defensive end.

``When we won 13 in a row, the defense was much better,' Mavericks center Brendan Haywood said. ``We have to improve our intensity on defense.'

The Thunder expanded an eight-point halftime lead to 13 in the third quarter, and took a 94-85 edge into the final quarter.

Oklahoma City was ahead by 19 early in the fourth quarter before a 17-2 run by Dallas - capped by Nowitzki's two free throws with 2:40 left - pulled the Mavericks to 110-106.

J.J. Barea made one of two free throws with 52.7 remaining to get Dallas to 113-109, but Eric Maynor's 3-pointer from the left wing with 28.9 seconds left gave Oklahoma City a 116-109 advantage.

``I was open for the shot and the shot clock was going down and I was able to knock it down,' said Maynor, who had 14 points. ``Teammates trust in each other, that's how it works.'

Dallas was in front 37-35 after one quarter, setting a season high for the opening quarter and shooting 75 percent (15 of 20) from the floor. The bad news for the Mavericks: the Thunder burned Dallas' defense for 14 of 24 from the field, getting 10 points each from Durant and Green.

``We had a great offensive quarter, 37 points is a huge number,' Mavericks coach Rick Carlisle said. ``But our defense was very disappointing.'

Oklahoma City kept attacking the basket and opened the second quarter with a 14-3 run en route to a 67-59 halftime lead, the Thunder's highest-scoring half of the season.

The Thunder were perfect on their first 23 foul shots before Maynor missed late in the third quarter,

Mavericks starting forward Shawn Marion sat out the second half because of a left oblique strain and is day-to-day.

Marion, who finished with eight points in 15 minutes, missed a solo layup in the second quarter and went back on defense holding his left side.

Carlisle said the injury is not considered serious.

NOTES: Oklahoma City has won five of six overall. ... The teams split the season series 2-2 . ... The Mavericks have already clinched a playoff berth. ... Dallas F Eduardo Najara has been bothered by a recent back problem but he had 11 points in 13 minutes. ... Dallas Cowboys QB Tony Romo sat courtside.