The loss continued a poor run for the fourth-ranked Pegula, who won her opener in Montreal over Maria Sakkari of Greece, but exited Wimbledon and the D.C. Open after one match in July.
Sevastova will take on Naomi Osaka, who moved to the fourth round with a 6-2, 6-4 win over 22nd-seeded Jelena Ostapenko of Latvia.
Osaka, a former No. 1-ranked player from Japan, hit five aces and converted 6-of-9 break point opportunities to win the match in 1 hour, 12 minutes.
In other daytime results, 16th-seeded Clara Tauson of Denmark rolled to a 6-3, 6-0 third-round victory over Ukraine’s Yuliia Starodubtseva.
Wimbledon champion Iga Swiatek, the tournament’s No. 2 seed, headlined the night session. She was scheduled to face Eva Lys of Germany in third-round action.
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AP tennis: https://apnews.com/hub/tennis