Ivo Karlovic and Lukas Rosol both survived scares as they progressed to the quarter-finals of the Nastase Tiriac Trophy on Wednesday.
Third seed Karlovic came from a set down to see off teenage Croatian compatriot Borna Coric 3-6 6-3 6-4 at the clay-court tournament in Bucharest.
"It was my first match on clay this year," Karlovic said. "I didn't start too well, but set after set I was feeling better.
"It was really cold, especially because I came here from the States. Normally I really like playing teenagers, because they don't know my game, but he is also Croatian and it was difficult."
Karlovic will meet seventh seed Jiri Vesely in the last eight after the Czech easily beat Malek Jaziri 6-3 6-1.
Meanwhile, fourth seed Rosol needed two hours and 37 minutes to overcome Dusan Lajovic 4-6 6-4 6-3.
"It was a good match for me, in difficult conditions, the weather changing, not easy," Rosol said. "But in the end I was the happy one. And this is the most important.
"I remember that I played [Lajovic] in Indian Wells last year and won in three sets. I'm happy that I found again the way to beat him. He is a very good player."
Rosol will now face fifth seed Guillermo Garcia-Lopez following the Spaniard's 7-5 6-2 success against Marcos Baghdatis.