Reigning champion Timea Babos and sixth- seeded Yanina Wickmayer of Belgium each won their first-round matches at the $235,000 Monterrey Open on Monday.
Babos ousted Mexico's Ana Sofia Sanchez 6-3, 6-3 on the hardcourts at Sierra Madre Tennis Club. The Hungarian beat Romanian Alexandra Cadantu in last year's Monterrey finale.
Wickmayer had a much stiffer test in Russian Valeria Savinykh, pulling out a 4-6, 6-1, 6-4 victory to advance.
Meanwhile, seventh-seeded Pole Urszula Radwanska snuck past American Maria Sanchez 6-2, 2-6, 6-2.
Others moving on were Galina Voskoboeva of Kazakhstan and Monica Niculescu of Romania. Voskoboeva earned a 6-3, 3-6, 6-3 win over Eleni Daniilidou, while Niculescu benefited from Kimiko Date-Krumm retiring in the second set.
Fifth-seeded Anastasia Pavlyuchenkova was losing 4-2 in the first set against Nina Bratchikova before play was suspended for rain.
The top seeds here are German left-hander Angelique Kerber and 2009 champion Marion Bartoli of France.
This week's Monterrey champ will collect $40,000.