OKLAHOMA CITY — Kevin Durant scored 37 points, Russell Westbrook added 28, and the Oklahoma City Thunder beat the San Antonio Spurs 113-99 on Thursday night to win the Western Conference semifinal series 4-2.

Steven Adams had 15 points and 11 rebounds, and Andre Roberson added 14 points for the Thunder.

Oklahoma City lost 124-92 in Game 1, but first-year coach Billy Donovan led the Thunder to victory in four of the next five. Oklahoma City will face defending NBA champion Golden State in the Western Conference finals, starting Monday in Oakland.

And the Spurs could head into an uncertain future after a franchise-record, 67-win season, with 40-year-old Tim Duncan struggling for much of the series before scoring 19 points as San Antonio tried to fight back in the fourth quarter.

Kawhi Leonard scored 22 points and LaMarcus Aldridge added 18 for the Spurs. San Antonio lost just once at home during the regular season, but the Thunder beat the Spurs twice in San Antonio during the series.

Oklahoma City opened up a 47-29 lead late in the second quarter after a 3-pointer by Westbrook that brought a roar from the crowd. Durant’s 3-pointer with 2.3 seconds left in the half pushed the lead to 55-31 at the break. Durant scored 18 points in the first half and Westbrook added 13.

The Thunder looked like the Spurs often do in the first half, running an efficient offense and shooting 46.5 percent from the field while committing just three turnovers before the break.

It was a season-low point total for the Spurs in a first half. San Antonio shot 31.1 percent from the field before the break and missed all nine of its 3-pointers.

Oklahoma City kept the pressure on and led 91-65 at the end of the third quarter.

The veteran Spurs had one last surge left and got as close as 11, but a 3-pointer by Westbrook, then a driving layup by Westbrook, killed San Antonio’s momentum for good.