Collins, the 2022 Australian Open runner-up, had 39 winners and was 6-for-6 on break points in outdueling Volynets. Leading 5-4 in the second set, Volynets served for the match but Collins stymied her, won the tiebreaker and then dominated the final set.

Collins will face sixth-seeded Xiyu Wang of China on Friday. Wang sailed to a 6-1, 6-2 victory over Darja Semenistaja of Latvia.

Both US players in action Thursday night lost their second-round matches. Latvia's Anastasija Sevastova routed second-seeded Sloane Stephens 6-3, 6-2, and Slovakia's Anna Karolina Schmiedlova beat Sachia Vickery 5-7, 7-6(5), 7-5.

San Diego Open

Anna Blinkova of Russia saved five of eight break points while beating fifth-seeded Dayana Yastremska of Ukraine 7-6(6), 6-2 to reach the quarter-finals. Yastremska led 5-2 in the first set before Blinkova rallied to force a tiebreaker. Blinkova won the final two points to win the set and sailed through the second for the victory.

Donna Vekic of Croatia also advanced with a 6-4, 3-6, 6-3 victory over Canada's Marina Stakusic. The 19-year-old Stakusic had six aces.

Third-seeded Emma Navarro of the United States logged a 6-3, 3-6, 6-1 win over the Czech Republic's Katerina Siniakova, and Russia's Anastasia Pavlyuchenkova came from behind to defeat China's Xinyu Wang 4-6, 7-6(5), 6-2. Pavlyuchenkova needed four set points to take the second set, then later sealed the victory on her fourth match point.