Eric Mayor helped seal the victory with a 3-pointer during the final minute, and Russell Westbrook and Nick Collison scored 17 points each for the Thunder -- who will be appearing in the post-season for the first time since the franchise moved from Seattle to Oklahoma City.
The Thunder -- sixth in the Western Conference -- won for a third straight time and for the fifth time in six games.
Dirk Nowitzki led the Mavericks with 30 points and 13 rebounds. Jason Kidd scored 24 for Dallas, which ended the day in a four-way tie with Utah, Phoenix and Denver, 5 1/2 games behind the first-place Los Angeles Lakers in the West.
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