World number five Maria Sakkari advanced to the last four of the WTA Finals for the second straight year on Wednesday as Tunisia's Ons Jabeur got her campaign back on track with a battling victory.
Greece's Sakkari secured her place in the semi-finals in Fort Worth, Texas, after cruising past seventh-seeded Aryna Sabalenka of Belarus 6-2, 6-4.
Sakkari's second win of the round-robin stage left her on top of the Nancy Richey Group with one match remaining.
Sakkari will qualify in top spot from the group if she beats Jabeur in her final first-round game.
"It feels great, just giving myself the chance to play my next match a little bit more relaxed, and enjoy another battle," Sakkari said after her win.
"Obviously I want to win — I still want to go undefeated. It's gonna be a very tough match but it's nice to feel like my hard work is paying off finally," she added.
Jabeur, who had been beaten by Sabalenka in three sets on Monday, shrugged off that loss with a spirited 1-6, 6-3, 6-3 victory over Jessica Pegula of the United States.
Sabalenka will pip Jabeur for a semi-final berth if she beats Pegula in her final group game.
Pegula was left ruing her failure to capitalize on a fast start in her defeat to Jabeur, a losing finalist at Wimbledon and the US Open this year.
The American roared through the opening set, winning six straight games after dropping the first.
Jabeur responded with an early break for a 2-1 lead in the second before dropping her serve at love.
Jabeur managed to right the ship, breaking twice in a row to force the third set.
The decider was tightly contested, Pegula failing to convert five early break points.
Jabeur finally gained the upper hand with a break for 5-3 and polished off the win after an hour and 41 minutes.
"After the first set, she was playing really well and really fast," Jabeur said.
"The balls were tough, very low. I know she likes to play the balls like that. And I just had to find that click to just change up the rhythm and impose my game."
Pegula was surprised to discover that she was not yet mathematically eliminated, although it would take an unlikely combination of results to see her reach the semi-finals.
"I'm still in?" Pegula asked a questioner at a post-match press conference. "That's good to know. I'm still alive, somehow."