Estoril, Portugal (SportsNetwork.com) - Second-seeded Kevin Anderson was a second-round upset victim Thursday at the inaugural Estoril Open tennis tournament.

In-form Spaniard Guillermo Garcia-Lopez took out the 6-foot-8 South African slugger Anderson in 6-4, 3-6, 6-1 fashion on the red clay at Estoril Tennis Club. Anderson piled up nine double faults to hurt his own cause.

Garcia-Lopez is fresh off his clay-court title in Bucharest last week and has now won his last seven matches.

Meanwhile, eighth-seeded Gilles Muller of Luxembourg avoided an upset by coming from behind to beat tough Spanish clay-courter Albert Montanes 4-6, 6-3, 7-6 (9-7).

"Spending this much time on the court gives me confidence," said Muller. "I'm starting to feel pretty comfortable now on the clay, sliding around and moving around."

Other second-round results saw rising 19-year-old Croat Borna Coric hold off Portuguese wild card Rui Machado 6-4, 5-7, 6-1 and Pablo Carreno Busta drill lucky-loser and fellow Spaniard David Vega Hernandez 6-1, 6-2. Vega Hernandez made his ATP debut after entering the draw when third- seeded former top-10 star Tommy Robredo of Spain withdrew.

Friday's quarterfinals in Estoril will pit fifth-seeded Frenchman Richard Gasquet against Spaniard and fellow former top-10 performer Nicolas Almagro; seventh-seeded Aussie Nick Kyrgios versus Dutchman Robin Haase; Muller against Carreno Busta; and Coric versus Garcia-Lopez.