Earlier, four-time Grand Slam champion Naomi Osaka won 6–2 6-4 over 22nd seed Jelna Ostapenco.
Osaka said, “He broke me a couple of times, but he is actually a good return, so I can’t take it personally.”
Japan’s Osaka, a twice in the US and Australian Open, will play Anastasia Sevastova after a winner, 35-year-old distressed defending champion and third seed Jessica Pagula 3-6 6-4 6-1.
The American Pegula was on the 11-match winning run in Montreal, but an error-dal gave him the cost against World No. 386 Sevastova to take a decision.
Like Osaka, Sevastova, Latvia, returned from maternity leave in early 2024 and has now registered its first win over a top-five rival since 2017.
“It was a strange match for me,” said Pegula. “I felt as if I had total control and then I played some terrible games like three games.
“It completely flipped the match speed, and I went to a set and 2–0 to be down very quickly.
“I really don’t think I am playing great tennis. Many times I am, but I feel very up and down, a kind of dirty, which I don’t like. I have received it to find out.”
