Ajla Tomljanovic reached her first WTA Tour quarter-final but acknowledged she had mixed emotions after Bethanie Mattek-Sands retired hurt in the third set of their second-round clash at the WTA Bell Challenge in Quebec City.
The pair had been doing battle for more than two hours when, with Tomljanovic leading 7-5 3-6 4-1, fourth-seeded American Mattek-Sands fell and could not continue.
"She slipped and her knee is in bad shape," the 20-year-old Croatian told the WTA Tour's official website. "Winning this match is bittersweet. I feel really bad for her.
"She hasn't had an easy road. I hope she recovers as soon as she can."
Tomljanovic will face Marina Erakovic, the eighth seed from New Zealand, in the last eight.
Second seed Kristina Mladenovic of France was also the beneficiary of a retirement. She led Petra Martic 6-3 2-3 when the Croatian halted proceedings due to illness.
Mladenovic will face Eugenie Bouchard in the quarter-finals after the Canadian fifth seed despatched Kazakh qualifier Sesil Karatantcheva 7-6 (7/2) 6-4.
Third seed Lucie Safarova of Czech Republic sent down 13 aces and saved five set points in the second-set tie-break en route to a 7-6 (7/4) 7-6 (12/10) victory over Croatia's Mirjana Lucic-Baroni.
Next up for Safarova is a meeting with seventh-seeded American Lauren Davis, who edged a topsy-turvy encounter with Czech Andrea Hlavackova 6-1 2-6 6-3.