Fourth-seeded Marin Cilic of Croatia advanced to the second round of the St. Petersburg Open on Tuesday, while defending champion Mikhail Kukushkin of Kazakhstan made an early exit.
Kukushkin, who was looking for his second title, lost to Michael Berrer of Germany 6-1, 4-6, 6-4. Julien Benneteau of France also advanced with a straight-sets victory over Pere Riba of Spain, 6-2, 6-1.
The 22nd-ranked Cilic, aiming for his first title this season, defeated Ukrainian qualifier Sergei Bubka 6-4, 7-6 (1). Cilic broke in the ninth game of the first set. Bubka saved five break points in the 11th game of the second set before the Croat prevailed in the tiebreaker to win on his first match point.
In a later match, Alex Bogomolov Jr. of the United States will face Igor Kunitsyn of Russia.