World number one Aryna Sabalenka defeated Elena Rybakina to secure her place in the last four of the season-ending WTA Finals in Cancun, Mexico.
Sabalenka led 6-2 3-5 against Rybakina when play was suspended at 23:40 local time on Thursday due to stormy weather.
The Kazakh levelled the tie within two minutes of play being resumed, but Sabalenka eventually claimed a 6-2 3-6 6-3 victory.
"I didn't really think a lot about this match," she told Tennis Channel.
"I was just like, whatever. I'm going to go out there and do everything I can and if I win, I win and if I lose, I go home on vacation.
"I was just trying to play as good as I can."
The Belarusian, who is set to retain her world number one ranking if she reaches the final, joins American group winner Jessica Pegula in the semi-finals.
Rybakina and eighth-seeded Greek Maria Sakkari are eliminated from the group stage.
All four players in the other group are still in contention for the semi-finals.
US Open champion Coco Gauff faces Wimbledon winner Marketa Vondrousova, while world number two Iga Swiatek - this year's French Open champion - is up against Ons Jabeur later on Friday.