Seeded players Andreas Seppi, David Nalbandian and Gilles Muller won in straight sets to advance to the quarter-finals of the Serbia Open on Wednesday.
The second-seeded Seppi defeated Ivan Dodig of Croatia 6-4 6-4, fourth seed Nalbandian beat qualifier Aljaz Bedene 6-4 6-3 and eighth seed Muller downed Eduardo Schwank 6-3 7-6 (7-0).
Joao Souza from Brazil also advanced after wild card Dusan Lajovic retired because of an ankle injury.
Top-seeded Pablo Andujar will face Filippo Volandri on Thursday.
Last year’s champion, top-ranked Novak Djokovic, has pulled out of the tournament that is organised by his family.