Tauson won her lone tour title in New Zealand in January, beating fellow Montreal quarterfinalist Naomi Osaka of Japan in the final.
Keys outlasted 11th-seeded Karolina Muchova of Czechia 4-6, 6-3, 7-5 in the windy afternoon session.
Osaka also advanced in the afternoon, routing Anastasija Sevastova of Latvia 6-1, 6-0 in 49 minutes — the second-fastest victory of her career. Osaka had a 42-minute victory in a 2016 event in Brazil.
Osaka reached the final eight of a WTA 1000 or Grand Slam event for the first time in 19 months. On Tuesday, she will face the winner of a night match between fifth-seed Amanda Anisimova of the United States and 10th-seeded Elina Svitolina of Ukraine.
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AP tennis: https://apnews.com/hub/tennis