Russia's Anastasia Pavlyuchenkova, the No. 2 seed, and France's Caroline Garcia, the No. 3 seed, won their opening matches at the Monterrey Open, advancing to the second round at the hard-court event in northern Mexico.
Pavlyuchenkova beat Germany's Tatjana Maria 6-1, 6-3, while Garcia knocked off Mexican teenager Renata Zarazua 4-6, 6-2, 6-3 on Monday.
The 25-year-old Pavlyuchenkova, a three-time champion in Monterrey, needed just 70 minutes to win her match and will play the winner of the match between American Kristie Ahn and Slovakia's Jana Cepelova in the second round.
Garcia, who is ranked 24th in the world, will face the winner of the contest between American Madison Brengle and Argentina's Nadia Podoroska.
The 23-year-old Garcia had some problems with Zarazua, who is ranked 304th in the world, and needed an hour and 50 minutes to put away the 19-year-old Mexican.
On Tuesday, German world No. 1 and top seed Angelique Kerber will play Italian veteran and 2010 French Open champion Francesca Schiavone, who is ranked 152nd in the world.
Spain's Carla Suarez Navarro, the No. 4 seed, will take on Belgium's Alison Van Uytvanck, while Hungary's Timea Babos, the No. 5 seed, will play the Netherlands' Lesley Kerkhove.
Russia's Ekaterina Makarova, the No. 6 seed, will play the Czech Republic's Denisa Allertova; France's Alize Cornet, the No. 7 seed, will take on Russia's Irina Khromacheva; and American Christina Mchale, the No. 8 seed, will play Czech Tereza Martincova.
European players have dominated at the Monterrey Open in recent years.
France's Marion Bartoli won the title in 2009; Pavlyuchenkova took home the trophy in 2010, 2011 and 2013; Babos won in 2012; Serbia's Ana Ivanovic won the championship in 2014; and Switzerland's Timea Bacsinszky won in 2015.
Last year, Britain's Heather Watson won the Monterrey Open.