Top seed Janko Tipsarevic and second seeded Juan Monaco reached the Stuttgart claycourt semi-finals on Friday with the top-ranked Serb surviving a gruelling quarter-final against German Bjorn Phau.
Tipsarevic saved four match points as he claimed a 6-7 (6/8), 7-6 (7/2), 6-4 victory in just under three hours.
"I'm a little bit lucky that I managed to win the second set and save four match points," admitted Tipsarevic.
"I kept calm in the third set and I was playing good. We were out on the court so long and it's not easy to close out the match no matter who you're playing. He went for a little bit too much on two occasions, but on the other two match points I think I played well."
The 28-year-old Tipsarevic will face Brazil's Thomaz Bellucci, who defeated Germany's Cedrik-Marcel Stebe 6-4, 6-1, in the semi-finals.
Monaco eased past Slovakian qualifier Pavol Cernevak 6-1, 7-5.
Monaco, the world number 14 from Argentina, will next meet Spaniard Guillermo Garcia-Lopez, who thumped German wildcard Dustin Brown 6-0, 6-3.