Eighth seed Sam Querrey crashed out of the Geneva Open in the first round as he was beaten in straight sets by Guillermo Garcia-Lopez.
American Querrey sent down 13 aces in Monday's encounter but that was not enough for the world number 37 to progress as he slumped to a 7-6 (7-5) 6-4 defeat.
There was better news for compatriot Steve Johnson, the seventh seed seeing off Mikhail Youzhny 6-3 7-5 while Federico Delbonis overcame wildcard Janko Tipsarevic 6-1 7-6 (8-6).
Ernests Gulbis got the better of a player ranked 24 places above him to reach round two, the world number 76 seeing off Ricardas Berankis in a tightly contested battle 7-5 7-5.
Lukas Rosol needed less than an hour to seal his progression on the clay in Switzerland with a straightforward 6-3 6-4 defeat of qualifier Roberto Ortega-Olmedo.
Elsewhere in the draw, Pablo Carreno Busta and Inigo Cervantes joined countryman Garcia-Lopez in the second round with wins over qualifiers Christian Garin and Andreas Beck respectively.