Mirjana Lucic-Baroni and Monica Puig reached the Abierto Mexicano Telcel second round as Eugenie Bouchard bowed out on Tuesday.
Top seed Lucic-Baroni, making her first appearance since her fairytale run to the Australian Open semi-finals, proved too good for Belinda Bencic 7-5 6-4.
Bencic, 19, had beaten the Croatian twice previously, but the 34-year-old broke seven times to clinch victory at the WTA International event.
It was another good day for the seeds in Acapulco.
Puig battled past Italian veteran Francesca Schiavone 6-4 7-6 (7-4) and Jelena Ostapenko cruised to a 6-2 6-2 win over Danka Kovinic.
The fifth-seeded Christina McHale, the 2014 runner-up, beat French qualifier Fiona Ferro 6-4 6-4.
The only seed to fall was Bouchard, who suffered a surprise 7-6 (7-4) 6-1 loss to Ajla Tomljanovic.
It marked a first WTA Tour win since 2015 for Tomljanovic, who was making her return from injury.
Daniela Hantuchova made the most of her wildcard, the Slovakian beating Yanina Wickmayer 4-6 6-3 6-2.
Julia Goerges battled past Kateryna Bondarenko 2-6 6-4 6-3 and Madison Brengle edged Annika Beck 4-6 6-3 6-2.
In a clash between two American qualifiers, Taylor Townsend overcame Jennifer Brady 7-5 7-6 (7-4).