Aryna Sabalenka and Alexander Zverev kept their Indian Wells title bids alive on Thursday, dispatching their respective opponents to book semi-final berths at the desert hardcourt tournament.
Sabalenka beat rising Canadian Victoria Mboko 7-6(0) 6-4, while Zverev made light work of Frenchman Arthur Fils 6-2 6-3.
The world number one Sabalenka was pushed hard by 19-year-old Mboko, whose explosive strides and aces levelled the opening set at 5-5 and forced a tiebreak.
But Sabalenka's mental fortitude proved decisive, winning the tiebreak to love — a first in her career.
"I'm happy with the win, even though a couple of things weren't really working well today. I still managed to win though. I don't think she broke me," the 27-year-old Belarusian player said after the match.
"She (Mboko) is definitely a future Grand Slam champion. It's incredible to see how brave these young girls are these days. They go out there and go after their shots. They're aggressive and they fight. It's incredible to see."
The second set followed a similar script: Sabalenka led 4-2, Mboko clawed back to 5-4 threatening another tiebreak, but the four-time Grand Slam champion closed it out to reach the semi-final.
The teenager fell agonizingly short of what would have been a historic fifth top 10 win of the year and the first by a Canadian woman over a world number one.
Zverev, meanwhile, was a model of efficiency against Fils, committing only 17 unforced errors to the Frenchman's 27 and just one double fault compared to his opponent's four.
The German fourth seed never looked troubled and will now turn his attention to a maiden Indian Wells title.
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