Top seed Tommy Haas was pushed all the way by Horacio Zeballos before coming through in three sets to make the Brazil Open semi-finals.
The Argentine ran out of steam in the third set after levelling the match, going down to a 6-3 5-7 6-2 by Haas, who avoided an upset to make the last four.
Fourth seed Juan Monaco wasn't so lucky though, as he was dumped out by a surprise loss to Italian Paolo Lorenzi, who won 7-6 6-7 6-4 to make his very first ATP Tour semi-final.
After Haas lost to Marin Cilic in last month's Croatia final, he is determined to go on to win a title but knows Lorenzi will be a dangerous underdog.
"Lorenzi has been around for a long time so this is a goal I'm sure he has been waiting to achieve for a lifetime," Haas said.
"He has nothing to lose and is going to try to go one more and get to his first ATP tour final. He is a dangerous player. I'm going to have to try to play some of my best tennis."
World No 114 Lorenzi squandered a match point before losing the second set, but hit back to control the third with 12 aces in total helping him to a first semi-final after five quarter-final defeats in his career.
"I'm very happy to finally breakthrough to the semi-finals," Lorenzi said. "I've had a lot of opportunities before but was never able to come up with the victory at this stage. For sure this is one of my greatest weeks on the tour.
"It was a very close match, he had his chances in the first set and I had mine in the second, it was very difficult."
The win was even more impressive given Monaco has won the fifth-most matches on clay on Tour, but he will now have to wait for his 200th victory on the surface.
It will be Argentina v Brazil in the other semi-final, with home favourite Thomaz Belluci taking on Federico Delbonis after both men enjoyed easy straight sets wins.