Only two of the quarterfinal matches at the clay-court event have been determined.
Melzer, seeded sixth, defeated Leonardo Mayer in the second round 6-4, 6-2.
Nicolas Devilder had a 6-4, 4-2 advantage over Alexander Peya.
Victor Hanescu will meet Brian Dabul in Friday's quarterfinals and Potito Starace will take on Eduardo Schwank.
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