Former U.S. Open champion Juan Martin set victor, while third seed Gael Monfils came up a quarterfinal loser Friday at the $1.905 million Valencia Open 500 tennis event.

The sixth-seeded del Potro handled one-the-mend American Sam Querrey 6-2, 7-5 on the indoor hardcourts at Valencia's City of Arts and Sciences. The 6- foot-7 del Potro popped seven aces in advancing in 77 minutes, as Querrey failed to enjoy even one break-point chance against the punishing Argentine.

The 6-foot-6 Querrey was playing his first tennis this week sine mid-June after undergoing elbow surgery.

Del Potro's semifinal opponent on Saturday will be last year's Valencia runner-up Marcel Granollers, who grounded the French Monfils 7-6 (14-12), 3-6, 6-4 in 2 hours, 26 minutes Granollers saved four set points in the grueling opening-set tiebreak.

The world No. 10 Monfils, who's trying to qualify for one of the eight spots in the season-ending ATP World Tour Finals in London later this month, drilled 10 aces in a losing effort on Day 5.

Granollers lost to this week's top seed David Ferrer in last year's all- Spanish finale here.

The 2011 Valencia titlist will collect $455,000.