LAS VEGAS (AFP) — Victor Wembanyama made a triumphant return from injury to lead the San Antonio Spurs to a stunning National Basketball Association (NBA) Cup semifinal upset of the Oklahoma City Thunder on Saturday as the New York Knicks downed the Orlando Magic to book their place in the final.

French prodigy Wembanyama, who has missed the Spurs' last 12 games after suffering a left calf strain last month, produced a dominant performance at both ends of the court to set up a thrilling 111-109 victory at Las Vegas's T-Mobile Arena.

The 7-foot-4 21-year-old finished with 22 points, nine rebounds and two blocks in 21 minutes on court, helping the Spurs climb out of a 16-point hole in the second quarter to inflict only the second Oklahoma City defeat this season.

NBA champions Oklahoma City had gone into the game on the back of a 16-game winning streak, boasting a 24-1 record for the season that had prompted talk of them breaking Golden State's record 73-win season.

But after making a smooth start to control the game, Wembanyama began to make his presence felt off the bench in the second quarter to breathe new life into the San Antonio ranks. 

"I knew I had limited minutes so I had to make the most out of it," Wembanyama said. 

"Winning against a team like this, it might seem like it's just a game but it's a collective effort and it's not an easy thing.”

"It's only their second loss of the season. It means something."

Wembanyama was one of four San Antonio players to finish with double figures, with Devin Vassell scoring 23, and Stephon Castle and De'Aaron Fox adding 22 apiece.

"It says a lot. And it says a lot about where this team is going to be in the future," he said.

Reigning NBA Most Valuable Player Shai Gilgeous-Alexander led the Thunder scoring with 29 points, while Jalen Williams and Chet Holmgren added 17 points each.

In Saturday's other semi-final, Jalen Brunson scored 40 points to power the New York Knicks to their first NBA Cup final with a 132-120 win over the Orlando Magic.

The Knicks' in-form offense proved too hot for injury-hit Orlando as New York took their recent streak to nine wins from 10 games.

"We came out here and did exactly what we said we wanted to do, which was play Knicks basketball," said Karl-Anthony Towns, who backed Brunson with 29 points.

The Magic had led 36-33 after making a rapid start to a breathless opening quarter — earning the Knicks players some harsh and fiery words from coach Mike Brown in an early timeout.

"The way they came out, physicality-wise, we weren't ready for it," Brunson said. 

"We bounced back and responded to that, and the way we played the rest of the game is a testament to that first timeout."

New York went on a tear at the start of the second quarter, capitalizing on a missed floating jump shot from Desmond Bane to take the lead through Josh Hart.

The Knicks briefly relinquished their advantage soon after half-time, when Bane put the Magic back ahead with a running layup.

But Orlando ultimately could not keep pace with Brunson, who late in the third quarter left opposing guard Anthony Black sitting helplessly on the floor before executing a three-point step-back jumpshot.

Orlando's Jalen Suggs managed a team-high 26 points, but failed to complete the game after suffering with an apparent injury to his left side.

The Magic also felt the absence of Franz Wagner, their leading scorer this season.

The NBA Cup, a mid-season knockout tournament now in its third year, is proving a hit with audiences and players.

It now offers a tantalizing opportunity for the Knicks to win their first overall trophy since 1973.