Russian Samsonova, who has won 20 of her last 22 matches, smacked 21 winners and broke the powerful Belarussian four times en route to a 6-4, 2-6, 6-2 upset win over the world number four.

The WTA Finals featuring the world’s top eight players starts in Fort Worth on Oct 31.

Iga Swiatek, Ons Jabeur and Jessica Pegula had already locked up the first three spots before Guadalajara so with the addition of American Gauff and France’s Garcia, three openings remain.

Fifth seed Gauff was not at her best but was still good enough to see off Italy’s Elisabetta Cocciaretto 7-6(1), 6-3.

The American teenager double faulted five times and converted just four of 13 break opportunities but was the better player on the biggest points, rolling through the first set tiebreak and carrying that momentum into the second set.

“I’m just super excited,” said Gauff, 18, who will be the youngest player to compete at the WTA Finals since 2005.

“I wasn’t really thinking about it before the match, but I’m excited to join Jess (Pegula),” she said. The pair have also both qualified for the WTA Finals doubles tournament.

Wimbledon champion Elena Rybakina’s hopes of making the Finals ended after Pegula saved three match points to emerge with a 2-6, 6-3, 7-6(8) victory despite 14 aces from the Kazakhstani.

Rybakina would have qualified for the Finals if the WTA had issued ranking points at this year’s grass court major.

Danielle Collins and Jelena Ostapenko, who both have an outside shot of making the WTA Finals, won their second round matches yesterday, while other hopefuls including Madison Keys, Belinda Bencic and top seed Paula Badosa play later.