Aryna Sabalenka warded off the challenge of Victoria Mboko to progress to the semi-finals at Indian Wells.
Canada's Mboko was dangerous, especially in the first set. The 19-year-old pushed Sabalenka, the world No 1, with strong shots.
Mboko took the first set into a tiebreaker but then Sabalenka raised her level. The world No 1 won the tiebreak to love, the first time she's done that in her career.
Sabalenka secured a break to lead in the second set and, although Mboko fought back, she came through to win 7-6 (7-0) 6-4.
Defeat meant the teenager missed out on a potentially historic fifth top-10 win of the year and the first by a Canadian woman over a world No 1.
Sabalenka gave her opponent a ringing endorsement: "She 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," Sabalenka said afterwards.
"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."
Alexander Zverev beat Frenchman Arthur Fils 6-2 6-3 and take a place in the semi-finals.
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