Former champion Fernando Verdasco of Spain defeated Ernests Gulbis of Latvia 6-2, 3-6, 6-1 to reach the Croatia Open quarterfinals on Thursday.
Verdasco, the top seed and 2008 champ, converted five of 18 break points in the second-round victory.
Gulbis served eight aces but could not overcome Verdasco, who picked up his game in the third set.
"It was a difficult match," Verdasco said, describing Gulbis as "a player that hits the ball very hard and it is difficult to play against him."
"Hopefully it will be another good week like in 2008."
Verdasco will face Andrey Kuznetsov of Russia who defeated Mate Pavic of Croatia 7-6 (0), 6-1. Croatian wild card Pavic ousted sixth-seeded Juan Carlos Ferrero in the opening round.
Defending champion Alexandr Dolgopolov of Ukraine posted his fifth win in a row in Umag, defeating Italian Fabio Fognini in the second round 6-2, 6-4.
Dolgopolov, who last year won his first ATP title here, didn't drop serve.
Fifth-seeded Carlos Berlocq beat fellow Argentine Marco Trungelliti 7-6 (4), 4-6, 6-1. Berlocq converted eight of 16 break points, but his five double faults helped to keep Trungelliti in it.