Top seeds Mirjana Lucic-Baroni and Kristina Mladenovic booked spots in the Abierto Mexicano Telcel quarter-finals in contrasting fashion.
Lucic-Baroni, the Croatian veteran, outclassed American Shelby Rogers 6-4 6-4 in the second round in Acapulco on Wednesday.
The top seed, who recorded 33 winners, moved into the last eight, where Frenchwoman Pauline Parmentier awaits.
Parmentier claimed a 6-4 3-6 6-1 win over Andrea Petkovic, the German the only seed to fall.
Mladenovic, the French second seed, was forced into a marathon battle by Heather Watson.
The world number 30 eventually came through a 7-6 (7-4) 6-7 (5-7) 7-5 winner after three hours, 32 minutes.
Mladenovic's quarter-final opponent, Kirsten Flipkens, was only on court for 48 minutes.
Flipkens took the first set 7-5 before Ajla Tomljanovic, a shock winner over Eugenie Bouchard a day earlier, retired.
Lesia Tsurenko also made the most of a retirement, leading Julia Goerges 6-1 2-0 when the German called it quits.
Jelena Ostapenko was too good for Madison Brengle 7-5 6-4, 2014 runner-up Christina McHale beat Taylor Townsend 6-1 7-6 (7-5) and Monica Puig claimed a 6-4 6-4 win against wildcard Daniela Hantuchova.