Top-seeded Pablo Andujar of Spain, Andreas Seppi of Italy and David Nalbandian of Argentina won on Friday to reach the Serbia Open semi-finals.
France's Benoit Paire also advanced to the last four after beating third-seeded Jarkko Nieminen of Finland 0-6, 6-2, 7-5. Nieminen was playing his second match of the day, having beaten Croatian qualifier Antonio Veic 6-3, 4-6, 6-3 in a second-round match that was halted on Thursday at 5-3 because of rain.
Andujar defeated Lukas Rosol of the Czech Republic 6-4, 6-3 and will face Paire on Saturday.
Second-seeded Seppi beat eighth-seeded Gilles Muller of Luxembourg 6-4, 6-3, never losing serve and breaking his opponent three times. Seppi will face Nalbandian, who defeated Joao Souza of Brazil 6-3, 6-2. Nalbandian converted three of his four break points and dropped serve just once.