Juan Martin del Potro made a strong start to his French Open preparations with a 6-1, 6-0 hammering of Portugal's Rui Machado to reach the quarterfinals of the Estoril Open onThursday.

Del Potro, the top seed and defending champion, was playing an ATP match on the surface for the first time this season after winning two clay Davis Cup rubbers at home in April when Argentina defeated Croatia.

Despite the scoreline, the 23-year-old admitted that Machado had tested him as he looks to build up his form.

"I played well for only my first match after Davis Cup. The score might not have looked it, but he's dangerous on clay," said Del Potro, who won his last title at Marseille in February, prior to a semi-final in Dubai against Roger Federer.

" But I played much better than him and took all of my breakpoints."

A year ago, Del Potro arrived at the Estadio Nacionale ranked 46th and unsure of his game after missing much of 2010 following wrist surgery.

However, the 2009 US Open champion dug deep to claim his first title in the country with a victory over Spaniard Fernando Verdasco.

Now ranked a more respectable 12th, the Argentinian added: "I'm pleased with my performance. This was good for a first match of this part of the season."

Victory over Machado improved Del Potro's 2012 record to 24-6 ahead of his semi-final against two-time champion Albert Montanes on Friday.

Montanes, seeded seventh, advanced to the last eight with a 4-6,6-4,6-3 win over American Bobby Reynolds.

Fourth seed Albert Ramos of Spain beat German Bjorn Phau 7-5, 6-0 to reach the quarters, where he will face the last Portuguese in contention, Joao Sousa.

The local player won 3-6, 6-3, 4-2 when Uzbek Denis Istomin quit after a 30-minute evening rain interruption, citing a bad back as his reason for not returning to the court.

In the women's draw, Italian top seed Roberta Vinci reached the semifinals by defeating Russian seventh seed Nadia Petrova 6-2,1-6,6-4.

"I'm playing very well again this season," said 29-year-old Vinci, who won three clay trophies in 2011.

"It is some of my best tennis. I'm more consistent now than when I was young."

Estonian Kaia Kanepi, the number six seed, upset Czech fourth seed Petra Cetkovska 6-3,3-6,6-3.

Unseeded Carla Suarez Navarro defeated Spanish compatriot Silvia Soler-Espinosa 6-3, 6-3 to set up a meeting with Karin Knapp after the unseeded Italian defeated Galina Voskoboeva of Kazakhstan 7-6 (7/4), 2-6,6-4.