The Thunder flipped the script, and now they’re heading to the Western Conference finals.

Tim Duncan doesn’t know yet where he’s headed as the San Antonio Spurs face an uncertain future.

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

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 controlled Game 6, leading by as many as 28 points.

Westbrook said the Thunder never lost confidence.

‘‘We had that game, and we left it behind us,’’ he said. ‘‘We came out after that and had a different mindset. We knew what we had to do to win the series. They’re a great team. They've been winning for 10-plus years, same pace. I'm just proud of our guys.’’

Steven Adams had 15 points and 11 rebounds, and Andre Roberson added 14 points for the Thunder. Oklahoma City now will face defending NBA champion Golden State, starting Monday in Oakland, Calif.

‘‘Golden State’s a great team,’’ Donovan said. ‘‘It will be a great challenge. We've got a little bit of time to prepare before we play, but right now, for us, it’s just to enjoy the opportunity to move on, get a chance to continue to play and get as prepared as we can going into Game 1.’’

The Spurs were trying to extend the winningest season in franchise history after going 67-15. The 40-year-old Duncan struggled for much of the series before scoring 19 points as the Spurs tried to fight back in the fourth quarter.

Duncan didn’t clear anything up about his future after the game. He has a player option for next season.

‘‘I'll get to that after I get out of here and figure life out,’’ he said.

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.

‘‘We always give credit to our opponents, and obviously, OKC turned it up there and turned our execution into forced bad shots, and then we kind of trickled down from there and it snowballed,’’ Duncan said.

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Stephen Curry (29 points), Klay Thompson (33 points) and the Golden State Warriors eliminated the Portland Trail Blazers, 125-121, in Oakland, Calif., Wednesday night to take the semifinal series, 4-1, and advance to the Western Conference finals.