Lopez, ranked 32 in the world, defeated his Slovakian opponent in one hour 40 minutes to progress to a meeting with Netherlands' Igor Sijsling in the second round.
Top seed David Ferrer, granted a bye in the first round, will face Alex Bogomolov Jr next after the Russian beat British qualifier Dominic Inglot - a doubles specialist - 7-5 6-3.
Another Russian had success on Wednesday as Nikolay Davydenko beat Sanam Singh 7-5 6-3 to set up a meeting with Denis Istomin, who defeated sixth seed Pablo Andujar 6-3 6-2.
Seventh seed Julian Benneteau fared better as he reached the last eight with a 7-5 6-2 win over Matthew Ebden of Australia.
Vasek Posposil also secured a place in the quarter-finals when beating Michael Yani 6-3 7-5.
American Rajeev Ram was forced to retire with a hamstring injury when losing 7-6(4) 4-2 to Alejandro Falla.
- Alex Bogomolov Jr
- Igor Sijsling
- David Ferrer
- Dominic Inglot