Davydenko, seeded No. 1 in this tournament and ranked ninth in the world, defeated Alberto Martin 6-2, 6-3 in their second-round match.
No. 2 seed David Ferrer was upset by Nicolas Massu 4-6, 6-2, 6-4 on the clay surface.
Davydenko, a winner last week in Hamburg, will take on Simone Bolelli in the quarterfinals after Bolelli downed Fabio Fognini 6-3, 6-4.
Ivan Ljubicic pulled off an upset by defeating Nicolas Almagro 7-5, 7-6 (7-2), and fourth-seeded Jurgen Melzer cruised past Pablo Cuevas 6-4, 6-3.
Former world No. 1 Juan Carlos Ferrero, seeded fifth, rallied to defeat Potito Starace 1-6, 6-3, 6-2.
Copyright 2009 by United Press International.