Juan Martin del Potro overcame a difficult challenge in his first match at the Los Cabos Open, while defending champion Sam Querrey was eliminated.

Del Potro was tested in his opener but the top seed advanced to the quarter-finals 7-5 6-3 against American Marcos Giron on Wednesday.

Seeking his third ATP Tour title of the year, Del Potro – who reached the Wimbledon last eight – saved five of seven break points in his straight-sets victory over the qualifier.

Standing in the way of Del Potro and the semi-finals is unheralded Belarusian Egor Gerasimov.

Gerasimov upstaged fifth seed and titleholder Querrey 7-5 5-7 7-6 (8-6) at the ATP 250 tournament in Mexico.

Querrey fired down 23 aces but Gerasimov – who had not won a Tour-level match this year prior to this week in Los Cabos – managed to progress after two hours.

Last year's runner-up and eighth seed Feliciano Lopez was sent packing by Cameron Norrie 6-3 6-3, while Taylor Fritz lost 7-6 (7-3) 6-1 to Yoshihito Nishioka.

However, seeds Fabio Fognini, Damir Dzumhur and Adrian Mannarino survived.

Fognini (2) rallied past Quentin Halys 2-6 6-4 6-0, Dzumhur (3) defeated Thomas Fabbiano and Mannarino (4) accounted for Elias Ymer 6-0 6-2.

Rounding out the action, Michael Mmoh beat Peter Polansky 7-6 (7-1) 7-6 (7-2).