Seeds Anastasia Pavlyuchenkova, Danka Kovinic and Timea Babos all crashed out of the Abierto Monterrey Afirme on a rain-interrupted day.
Russian third seed Pavlyuchenkova was sent packing in the first round by qualifier Pauline Parmentier 6-2 6-2 in Monterrey.
Parmentier was leading 2-0 in the second set when rain - which forced the postponement of Caroline Wozniacki's match with Olga Govortsova without a ball being hit - halted proceedings before the Frenchwoman cantered to victory at the WTA event.
Monica Puig is next up for Parmentier after she defeated Marcela Zacarias 6-2 7-5.
Kovinic and Babos were also ousted in straight sets.
Montenegro's Kovinic - the seventh seed - was upstaged 7-5 6-2 by qualifier Nicole Gibbs.
Kovinic double-faulted on six occasions, while she was broken four times, despite fending off three break points against the American.
Awaiting Gibbs in the second round is countrywoman Christina McHale, who accounted for Victoria Rodriguez 6-0 6-4.
Eighth seed Babos lost out to Polona Hercog in a 6-3 6-2 defeat.
In other results, Yanina Wickmayer outlasted Johanna Larsson 6-2 4-6 6-1, Kirsten Flipkens downed Francesca Schiavone 6-3 7-6 (7-5), while Julia Glushko needed less than an hour to see off Alexandra Dulgheru 6-1 6-1.