Tunisian second seed Ons Jabeur earned her first victory at the WTA Finals as Maria Sakkari booked her place in the last four in Fort Worth.

Greek world number five Sakkari recorded a second straight-set win as she defeated Aryna Sabalenka 6-2 6-4.

It is the second year in a row that Sakkari has reached the semi-finals and she is the first player at this year's event to guarantee her progress.

World number one Iga Swiatek and France's Caroline Garcia both have the chance to secure their progress from the round-robin stage when they go head-to-head on Thursday.

Jabeur lost to Sabalenka in her opening match on her Finals debut but kept alive her hopes of progressing with the impressive comeback win against Pegula.

The 28-year-old, the first player from Tunisia to win at the season-ending event, meets Sakkari in her final group match.

"My first match, it was a few points, a few opportunities that were missing. I feel like this whole tournament is about who's going to seize those points to be able to win," said Jabeur.

"Because you never know. I lost my first match, and now I'm back in the game. One more match left. It's tricky and everyone's trying to give 100%.

"You don't have many opportunities, so you really have to focus."

Sakkari was the last player to qualify for this year's Finals but her back-to-back wins mean she is assured of a semi-final spot with a match to spare.