American Pegula has an excellent record in Canada – she was on an 11-match winning run in Montreal.
But she was shocked by world number 386 Sevastova who, like Osaka, returned from maternity leave in early 2024.
This was the 35-year-old’s first win over an opponent ranked in the WTA top five since beating Karolina Pliskova in 2017.
There was no hint of an upset when Pegula broke her in the opening game and again to love to claim the first set.
But a forehand winner earned Sevastova a break for a 5-4 lead in the second set and she denied Pegula three chances to break for a crucial hold to force a decider.
And when Pegula sent a down-the-line forehand wide to surrender a break and hand Sevastova a 2-1 lead, the Latvian did not let the momentum go.
She swept up the remaining games, including two further breaks, to claim a remarkable win in one hour and 41 minutes.
“It was a weird match for me,” said Pegula. “I felt like I had total control and then I just played a couple of terrible games for, like three games.
“That totally flipped the momentum of the match, and I went from being up a set and 2-0 to being down very quickly.
“I don’t really feel like I’m playing great tennis. At times I am, but I feel very up and down, kind of sloppy, which I don’t like. I’ve got to figure it out.”
