Top seed and defending champion Juan Martin del Potro was an untested second-round victor Thursday at the $525,000 Estoril Open tennis event.

The Argentine star leveled Portugal's own Rui Machado 6-1, 6-0 in 62 minutes at National Stadium. "Delpo" was not broken while breaking Machado five times in the predictable outing.

The former U.S. Open winner del Potro, who beat Spaniard Fernando Verdasco in last year's Estoril finale, will face another Spaniard, Albert Montanes, in Friday's quarterfinals. Montanes was a back-to-back Estoril champ in 2009 and 2010.

A seventh-seeded Montanes came from behind to beat American journeyman Bobby Reynolds 4-6, 6-4, 6-3 on Day 4.

Thursday's other second-rounders saw fourth-seeded Spaniard Albert Ramos defeat speedy German Bjorn Phau 7-5, 6-0 and Portuguese wild card Joao Sousa take out fifth-seeded Denis Istomin of Uzbekistan 3-6, 6-3, 4-2, retired.

The recent Casablanca runner-up Ramos and Sousa will tangle on Friday.

Friday's other quarterfinals will pit second-seeded Frenchman Richard Gasquet against Spanish qualifier Daniel Munoz-De La Nava and third-seeded Swiss Stan Wawrinka versus sixth-seeded Dutchman Robin Haase. Gasquet was an Estoril runner-up in 2007.

The winner of this clay-court French Open tune-up will claim $95,000.