Niemeier found out she was replacing Italy's Elisabetta Cocciaretto just 30 minutes prior to the match. After a slow start, she began clicking and scored on 61.1 percent (22 of 36) of her second-serve return opportunities in stunning Sakkari, the Greek woman ranked number nine in the world. Sakkari has dropped her last four matches.

Second-seeded Russian Liudmila Samsonova rolled to a 6-3, 6-1 victory over Spain's Sara Sorribes Tormo, and No. 4 Beatriz Haddad Maia of Brazil dispatched Germany's Tamara Korpatsch 6-1, 7-6 (6). Russia's Anna Blinkova was a 6-4, 6-2 winner over Bianca Andreescu of Canada and Russia's Diana Shnaider beat Germany's Angelique Kerber 7-5, 6-3.

Other winners were Katerina Siniakova and Linda Noskova of the Czech Republic. The marquee match between Ukraine's Elina Svitolina and Denmark's Caroline Wozniacki was suspended due to darkness with Svitolina leading 3-6, 7-6 (4), 2-1, and it will be resumed Tuesday.

Rothesay International

Number five seed Jelena Ostapenko of Latvia recorded a 7-6 (3), 6-1 victory over Belgium's Greet Minnen in the opening round of the Rothesay International in Eastbourne, England.

One entertaining matchup featured homeland wild card Harriet Dart facing the Czech Republic's Marie Bouzkova. The two matched up in a three-hour, 29-minute slugfest with Dart prevailing 7-5, 6-7 (7), 6-4.

Canada's Leylah Fernandez was a 6-2, 3-6, 6-2 winner over number seven seed Barbora Krejcikova of the Czech Republic. Poland's Magda Linette upset number eight seed Russian Anastasia Pavlyuchenkova 1-6, 7-6 (4), 6-4.

Also winning Monday were Ukraine's Anhelina Kalinina and China's Yuan Yue. Top-seeded Elena Rybakina withdrew prior to the round.