A thigh injury brought a premature end to Lesia Tsurenko's Miami Open challenge on Tuesday, sending Brazilian wildcard Beatriz Haddad Maia into the second round.
Abierto Mexicano Telcel champion Tsurenko was 3-2 and a break down to her 166th-ranked opponent when she decided she was unable to continue with her heavily strapped leg.
It was one of two retirements in quick succession on the opening day of first-round action, as Peng Shuai benefited from Danka Kovinic's withdrawal in the second set to seal her progression.
Sara Errani overcame a Belinda Bencic fightback in her opener, eventually prevailing 6-3 4-6 6-3 having looked on course for a straight-sets victory at two breaks up in the second.
Errani will now meet Zhang Shuai for a place in the third round.
TOP SEED KERBER AWAITS DUAN
The day opened with an impressive 7-6 (8-6) 6-3 victory for China's Duan Ying-ying over Laura Siegemund of Germany, with a second-round match against world number one Angelique Kerber her reward.
Venus Williams will face Haddad Maia, while Naomi Osaka's 6-2 6-3 win against Kristina Kucova earned her a meeting with third seed Simona Halep.
Mandy Minella beat Kristyna Pliskova 7-6 (7-4) 5-7 7-5 in one of the other standout matches of the day. She faces Svetlana Kuznetsova next.
Carina Witthoeft, Johanna Larsson and Lara Arruabarrena were among the other players to progress.