OKLAHOMA CITY -- For much of the season, the Golden State Warriors and San Antonio Spurs seemingly were on a collision course. The teams with the two best records in the NBA were predestined to meet in the Western Conference finals, while the up-and-down Oklahoma City Thunder were an afterthought.

However, after a grueling series against the Spurs, it is the Thunder who will face off with the defending champion Warriors for a chance to reach the NBA Finals.

Kevin Durant scored 37 points, and Oklahoma City earned the coveted spot with a 113-99 victory Thursday in Game 6 of the Western Conference semifinals at the Chesapeake Energy Arena.

Third-seeded Oklahoma City advances to face the top-seeded Golden State in the Western Conference finals. Game 1 is Monday in Oakland, Calif.

"Game 1 they just outplayed," Durant said of the Spurs, who won the series opener by 32 points. "Game 3, I think we gave the game away, and we didn't want to do that again. We were huge on the road, though. Russell (Westbrook) was huge last game. I think that propelled us into having a good game tonight.

"We're not done yet. We have to keep improving. Keep getting better and get ready for the next series."

Durant shot 12-for-24 from the field. He was a perfect 12-for-12 from the free-throw line and pulled down nine rebounds.

Westbrook posted 28 points and 12 assists, and Steven Adams added 15 points and 11 rebounds for the Thunder.

Kawhi Leonard paced the Spurs with 22 points on 9-of-23 shooting. LaMarcus Aldridge added 18 points and 14 rebounds. In what may have been his final game in the NBA, Tim Duncan scored 19 points in 34 minutes of action.

Duncan wasn't ready to announce his future plans after the game.

"I will get to that once I get out of here," Duncan said.

After trailing by 28 points, the Spurs cut the lead to 15 points with less than seven minutes in the game. Westbrook missed a layup, and Leonard dribbled the ball upcourt with all the momentum on San Antonio's side.

However, Westbrook came from the back to poke the ball away for the steal. Thunder guard Andre Roberson (14 points) threw the ball ahead to Durant, who was fouled while hitting a tough layup. The ensuing free throw pushed the gap back to 18 points.

The Spurs scored the next five points, including a layup by Duncan with 5:21 left in the game to cut lead to 97-84.

Durant then drove from midcourt to throw down a dunk. and the Thunder came up with back-to-back defensive stops before Danny Green nailed a 3-pointer to slice the margin to 12.

Durant turned the ball over, and Duncan took the ball in for a dunk. However, Thunder forward Serge Ibaka (eight points, 10 rebounds) came up with a blocked shot. That led to another dunk by Durant and a 101-88 advantage with 3:06 left.

San Antonio's David West hit a jumper, but Westbrook answered with a 3-pointer. After Leonard missed a shot, Westbrook connected on a layup to seal the win.

"I think to start the fourth, we kind of lost our way offensively. Got a little stagnant," Thunder coach Billy Donovan said. "We knew at some point they were going to make a run. They have too much character and are too good of a team. But our guys weathered it and got through it, and we found a way to close the game out."

The Thunder continued their rebounding dominance with a 50-40 advantage. They turned the ball over 12 times, while the Spurs gave the ball away just 10 times. Oklahoma City outshot San Antonio from the floor, 47.1 percent to 43 percent.

Oklahoma City is headed to the Western Conference finals for the fourth time in six years. The Thunder were 0-3 against Golden State in the regular season, but they are looking forward to taking on the defending champions.

"It's going to be fun," Durant said. "We're just excited to get this opportunity. Not too many teams get this opportunity. We're looking forward to it."

Duncan looked rejuvenated in the first quarter. He hit his first three shots from the field, and the Spurs had a quick 12-8 lead.

It didn't last long, though. Led by Westbrook and Durant, Oklahoma City gathered itself and began to attack the Spurs. The duo combined for 18 points in the quarter as the Thunder grabbed a 25-19 lead.

The Thunder bench subsequently took control of the first half. Waiters, Randy Foye and Enes Kanter came in and kept the pressure on the Spurs on both ends of the court and helped stretch the lead to 18 points. That included Waiters dishing out four assists.

With the Thunder leading by 24 at halftime, the Spurs started the second half with Duncan on the bench and Manu Ginobili in the starting lineup, and the change made a small dent in the margin.

"You have to play until the buzzer sounds," Durant said. "They are not going to give up. They are a class organization. They play hard every second. They pushed us all series. I know for both teams, it was a grind all series. They have so many great players. It was just a joy to match up with Kawhi Leonard for six games. I'm excited we came out here and played well."

NOTES: When the Thunder returned home after defeating San Antonio in Game 5, they were greeted by more than 500 fans after midnight at the airport. It left an impression on F Kevin Durant. "It's something I never even thought about when you want to be an NBA player, how dedicated the fans are, what you mean to the city," Durant said. ... Thunder coach Billy Donovan was asked why his team is doing better in the fourth quarter during the playoffs compared to the regular season. "It all comes down to defense," Donovan said. "I think if you look at our defense, our defense has been better in those situations."