Top seed Tomas Berdych has fallen at the first hurdle at the St Petersburg Open, losing 7-6 (7-5) 6-4 to Simone Bolelli in the second round.

The Czech world number five - enjoying a bye in the first round - was installed as favourite for the return of the ATP World Tour 250 series tournament and made a promising start as he opened up a 2-0 lead over his Italian opponent in the opening set.

Bolelli made his only break point of the set count as he restored parity midway through and Berdych proved unable to claw his way back after slipping 4-0 behind in the tie-breaker.

Berdych lost on his own serve in the third game of the second set and showed little sign of being able to change his fortunes, with Bolelli serving to love to wrap up an impressive victory.

Bolelli will now play Joao Sousa, who triumphed 6-3 6-3 over Marcel Granollers.

Second seed Milos Raonic faced no such problems as he saw off wildcard Evgeny Donskoy 6-4 6-4, setting up a quarter-final clash with Tommy Robredo, who beat Marcos Baghdatis 7-6 (7-5) 6-1.

Denis Istomin will face Dominic Thiem in the last eight following the former's 2-6 7-6 (7-5) 6-4 victory over Benjamin Becker.

Roberto Bautista Agut and Lucas Pouille will meet for a place in the semi-finals after their wins over Teymuraz Gabashvili and Jerzy Janowicz respectively.