STUTTGART, Germany (AP)—Simon Greul of Germany has upset Gilles Simon of France in straight sets to reach the quarterfinals of the Mercedes Cup.

The 73rd-ranked Greul beat Simon 6-4, 7-5 in the second round on Wednesday and will face Juan Carlos Ferrero of Spain or Argentina's Horacio Zeballos.

Zeballos was leading 7-6 (1), 6-6 when play was suspended for the day because of darkness.

Second-seeded Juergen Melzer of Austria defeated Germany's Mischa Zverev 7-5, 7-5 to set up a match with fifth-seeded Albert Montanes of Spain, who beat Argentina's Juan Ignacio Chela 7-5, 3-6, 6-2.