Britain's Naomi Broady progressed to the second round of the Monterrey Open, as compatriot Heather Watson suffered a seventh successive defeat.
World number 71 Watson was beaten in the first round of the Volvo Car Open in Charleston by American Taylor Townsend, 21, ranked 47 places lower.
Watson, 25, from Guernsey, has not won since reaching the semi-finals of the Hobart International in January.
Broady, 28, beat Canada's Carol Zhao 6-3 6-7 (5-7) 6-2 in Mexico.
The world number 136, who served 21 aces, will face Hungarian number four seed Timea Babos for a place in the quarter-finals.
Meanwhile, top-seeded world number three Garbine Muguruza beat wildcard Renata Zarazua to set up a second-round match with Alison Riske.
Number two seed Magdalena Rybarikova will play Jana Fett of Croatia after beating Risa Ozaki of Japan, while number three seed Lesia Tsurenko of Ukraine beat Nao Hibino to set up a tie with American Danielle Collins.