Swiss 18-year-old Belinda Bencic secured her second career title by winning the Rogers Cup as Simona Halep retired hurt in the final.
Bencic, who beat Serena Williams in the semi-final, came through 7-6 (7-5) 6-7 (4-7) 3-0 in Toronto.
Second seed Halep required treatment as she struggled with a leg injury and the extreme heat.
The Romanian said: "Sorry that I couldn't finish the match. I tried very much but it wasn't possible."
Bencic, who accounted for four of the top six seeds this week - Halep, Williams, Caroline Wozniacki and Ana Ivanovic - said on BT Sport 2: "Even if I would have lost it would have been an amazing experience."
Halep broke back from 5-3 down in the second set and won the tie-break to huge applause, but retired after losing her serve twice in the third set.
Bencic, who claimed her first title at Eastbourne in June, has won 21 of her past 25 matches and will move from 20th to 12th when the world rankings are announced on Monday.