Coco Gauff claimed just a second win in 13 meetings against Iga Swiatek to book her spot in the semi-finals of the WTA Finals in Saudi Arabia.

The American’s 6-3 6-4 victory also ensures Aryna Sabalenka will finish the year as world number one, with defending champion Swiatek no longer able to overtake the Australian Open and US Open winner.

The Pole, playing just her second match under new coach Wim Fissette, can still join Gauff in the semi-finals but she will need to beat Jessica Pegula in her final match.

Gauff’s only previous win over Swiatek came in Cincinnati last summer, with all 11 of her defeats suffered in straight sets.

Both players made errors throughout, and Gauff served 10 double faults in the second set, but she proved the stronger in the end, letting out a huge roar after breaking serve in the final game.

“It feels great,” she said in her on-court interview. “I had confidence going in, I felt like I was playing great tennis and even when I was playing a little bit sloppy the games that I lost were still going to deuce.

“That gave me confidence. If I stayed solid, I knew I had the chance to close out the match.”

In the earlier match, Wimbledon champion Barbora Krejcikova claimed her first WTA Finals singles victory and kept her semi-final hopes alive by beating Pegula 6-3 6-3.

The Czech, who lost all three matches on her only previous singles appearance, will take on Gauff on Thursday while Pegula can no longer progress.