Top seed David Ferrer eased through to the second round of the ATP Abierto Mexicano Telcel with a straight-sets victory over John Millman.
Ferrer - the reigning champion - needed just one hour, 22 minutes to get past his Australian opponent 6-4 6-2.
The Spaniard broke five times during the match and saved two of his own in a dominant performance as he searches for a fifth title at the hard-court event.
Ferrer will meet Alexandr Dolgopolov in the last 16 after the Ukrainian defeated Steve Johnson 7-5 7-6 (7-4).
Third seed Marin Cilic crashed out of the first round after losing in three sets against qualifier Ryan Harrison, who sits 120 places below him in the world rankings.
American Harrison won 83 per cent of points from his first serve as Cilic struggled with his second serve throughout the 3-6 6-3 2-6 loss.
Harrison faces Illya Marchenko in the second round following his 6-2 7-6 (7-4) victory over Tommy Paul.
Cilic was not the only seed to face elimination in the first round, with sixth seed Ivo Karlovic retiring against Aljaz Bedene with the match at 4-6 2-1.
Eighth seed Jeremy Chardy was also knocked out, with American Taylor Fritz securing a 6-4 3-6 6-3 win over the Frenchman.
Fourth and fifth seeds Dominic Thiem and Bernard Tomic avoided such fate, with 7-6 (7-3) 6-3 and 7-5 6-3 wins over Damir Dzumhur and Rajeev Ram respectively.
Thiem faces Dmitry Tursunov, who knocked out Sam Groth 6-4 3-6 7-5, in the next round, while Tomic will play Adrian Mannarino.
In other results, Sam Querrey eased past Dudi Sela 6-2 6-0 and will face Kei Nishikori in the last 16, while seventh seed Grigor Dimitrov set up a clash with Donald Young after defeating Denis Kudla 7-5 6-1.