The Sixers, playing for the second-straight night ran out of steam in the 110-105 defeat.
The teams were evenly matched all game, tied at 55 during the half and 101 at the end of the fourth.
Sixers point guard Jrue Holiday and Lou Williams made a large contribution with 22 points each -- with Williams points coming off the bench. Foward Elton Brand held his own with a double-double -- 13 points and 15 rebounds.
All-Star Kevin Durant led the Thunder with an impressive 34 points -- including a tying three late in regulation -- and 16 rebounds. Russell Westbrook added 27 points. the dynamic duo scored more than half of Oklahoma City's points.
The loss dropped the Sixers to 33-31 and ended their three-game winning streak.
And things won't get any easier as the Eastern-Confernce leading Boston Celtics come to town Friday night.
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