Second-seed Denis Istomin was shocked by Lukasz Kubot in the first round of the St Petersburg Open on Wednesday.
Uzbekistan player Istomin won the first set 6-4 but Polish ace Kubot hit back in the second set to win 6-3 before taking the decider 6-4.
Fourth-seed Fabio Fognini had to battle back from a set down to progress, beating Tobias Kamke of Germany 4-6 6-2 6-3.
Fognini's Italian compatriot Simone Bolelli also reach round two, overcoming Horacio Zeballos of Argentina 7-6 (7/3) 7-5.
Eighth-seed Jurgen Zopp of Estonia advanced when Russian qualifier Andrey Kumantsov, trailing 6-3 5-3 retired because of dizziness, while Ricardas Berankic of Lithuania led 6-2 3-3 when Philipp Petzschner of Germany also retired with a right knee injury.
Local player Igor Andreev, who was scheduled to face Sergiy Stakhovsky of Ukraine, withdrew because of a right shoulder injury sustained in Davis Cup action last week. Stakhovsky then beat Russian wildcard Ivan Nedelko 7-6 (7/2) 6-2.