Angelique Kerber kicked off her campaign to replace Serena Williams at the top of the WTA rankings with victory over Kristina Mladenovic in Cincinnati.
The German will become the new world number one if she wins the Western & Southern Open, from which Williams has withdrawn due to a shoulder injury.
Second seed Kerber set up a last-16 clash with Barbora Strycova - a 7-6 (13/11) 6-3 winner against Sam Stosur - by defeating France's Mladenovic 6-0 7-5.
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Just days after clinching an Olympic silver medal in Rio, Kerber told WTA.com: "It wasn't so easy to come to a tournament with just one or two days to prepare, and first rounds are always tough.
"But I was trying to play my game, and it's so nice to be back in Cincinnati. I have great memories from the last few years, and the fans are amazing."
Serena Williams (Wimbledon 2016)
Image credit: AFP
Britain's Johanna Konta progressed her bid to break into the WTA top 10 with a 6-2 6-3 success over Donna Vekic and will next face Agnieszka Radwanska.
The Polish former Wimbledon finalist saw off Andrea Petkovic 6-0 6-1 while third seed Simona Halep ousted Annika Beck 6-3 6-1 to secure a meeting with Daria Gavrilova, who beat 17th-seed Elina Svitolina 6-2 6-2.
French Open champion Garbine Muguruza was meant to play Coco Vandeweghe on Tuesday but heavy rain postponed their encounter, with the Spaniard claiming a 7-6 (7/4) 6-2 victory when the clouds cleared in Ohio. Her next opponent is Kurumi Nara's conqueror Anastasia Pavlyuchenkova.
Roberta Vinci will play Carla Suarez Navarro after the pair recorded respective wins against Tsvetana Pironkova and Alize Cornet.
Elsewhere, there were victories for 12th seed Timea Bacsinszky, Dominika Cibulkova, Timea Babos, Misaki Doi and Svetlana Kuznetsova.
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