Novak Djokovic and Rafael Nadal eased into the second round of the Abierto Mexicano Telcel in Acapulco but British No 3 Kyle Edmund crashed out against Sam Querrey.
Querrey, who is currently No 42 in the world, broke the 22-year-old twice in the opening set on his way wrapping it up 6-2.
But Edmund fought back and secured the only break of the second set to level the match up.
Querrey though took advantage of one of the two break points he had during the deciding set, while saving all four he faced to claim a 6-2 4-6 6-3 victory.
Elsewhere, top seed Djokovic saw off Slovakian Martin Klizan in a straight sets 6-3 7-6 victory, while Nadal did likewise, defeating German Mischa Zverev 6-4 6-3.
Marin Cilic, Nick Kyrgios and David Goffin all also progressed to the last 16 in Mexico, defeating Alexandr Dolgopolov, Dudi Sela and Stephane Robert respectively.
Last year's champion Dominic Thiem is also through having defeated Frenchman Gilles Simon, while Olympic silver medallist Juan Martin del Potro and 21-year-old Yoshihito Nishioka also booked their passages.
Paolo Lorenzi, Jordan Thompson, Borna Coric, Ernesto Escobedo, Steve Johnson, Adrian Mannarino and Donald Young make up the rest of the last 16.
The pick of the last-16 ties sees Djokovic face Del Potro, while Edmund's conqueror Querrey will face Goffin.
