Lopez defeated seventh-seeded Jeremy Chardy 6-7 (2-7), 7-5, 6-2 behind a 22-ace attack. Lopez didn't face a break point after the first set, winning 78 percent of the points on serve in the second and third sets.
No. 6-seeded Radek Stepanek, the only other seeded player in Tuesday's schedule, stopped Guillermo Garcia-Lopez 6-2, 6-3 by cashing in all four of his break opportunities. He lost the only break point he faced but still won more than two-thirds of the points on serve.
Qualifier Ryan Harrison was up 2-1 in the first set when Roberto Bautista Agut retired from the match. Harrison advances to a second-round match against top-seeded John Isner.
Jarkko Nieminen needed just 41 minutes to dispatch Bjorn Phau 6-0, 6-1. Nieminen dropped only six points in seven games serving and won 74 percent of the points in the match.
Also Tuesday, Kevin Anderson beat Aljaz Bedene 6-3, 3-6, 6-3; Fabio Fognini rolled past Grigor Dimitrov 6-3, 6-1; John Millman ousted Tommy Robredo 6-3, 6-4; and Bernard Tomic topped Marinko Matosevic 6-3, 6-4.