Romania's Simona Halep (30) fought off a late rally from Coco Gauff (18) to secure a nervy 6-4 7-6(2) win on Friday and advance to the Canadian Open semi-finals for a fifth time.
Twice champion Halep, up a set and leading 4-1 in the second, looked headed for an easy passage into the last four.
But Gauff dug in and rallied to force the second set to a tie break before 15th-seeded Halep finish off the 11th seed in the tie break to maintain her dominance over the American.
In four career meetings, including three this year, Gauff has yet to take a set off Halep, who now awaits either American seventh seed Jessica Pegula or Kazakh Yulia Putintseva.
Follow the final rounds in Toronto with Flashscore.
