Garcia-Lopez was up against it from the outset as he lost the first set heavily and, despite the second being more competitive, he was beaten 6-1 6-3. Estonian Zopp failed to serve out the match at 5-2 but immediately broke for the fourth time in the set to progress to a clash with American Wayne Odesnik.
Eighth seed Blaz Kavcic was another notable casualty as he was hammered by qualifier Antonio Veic.
The Croatian made light of a 60-place gap in the world rankings by blowing away his more-fancied opponent 6-1 6-2 in 67 minutes to set up an encounter with Lukas Rosol, who made his name by knocking Rafael Nadal out of Wimbledon this year.
There was no such setback for fifth seed Martin Klizan, though the Slovakian was made to battle through three sets before finally seeing off Austria's Dominic Thiem.
A one-sided first set gave no hint of the difficulties in store for Klizan, but world number 442 Thiem levelled and the players traded breaks in the deciding set before Klizan eventually completed a 6-1 3-6 7-5 win.
Filippo Volandri beat fellow Italian Alessandro Gianessi 1-6 6-4 6-3, while Hungary's Attila Balasz beat Austrian wildcard Martin Fischer 6-3 1-6 7-6 (7/2).