Daniel Gimeno-Traver shocked top seed Gilles Simon to seal his place in the semi-finals of the Nastase Tiriac Trophy.
Spaniard Gimeno-Traver, who reached the final of the Grand Prix Hassan II earlier this month, came from behind to progress to the last four with a 6-7 (5-7) 6-4 6-2 victory at the clay-court event on Friday.
He will now face seventh seed Jiri Vesely after the Czech overcame third seed Ivo Karlovic 6-4 6-4 to reach his third semi-final of the year.
"I have confidence and I'm looking forward to advancing to the final if possible," Vesely said.
"I took some advice after the previous match [against Ivo] in Dusseldorf last year. I was prepared to play two or three tie-breaks, if necessary, but I'm happy that I was able to convert when break opportunities occurred."
Meanwhile, fifth seed Guillermo Garcia-Lopez is also through to the semis following his triumph against fourth seed Lukas Rosol in a reversal of the 2013 final result, winning 6-4 7-6 (9-7).
"I tried to be more aggressive than I was in the final two years ago," Garcia-Lopez said.
"He [Rosol] likes to dictate the points. I am in the semi-final, it's normal to be more confident than a few weeks ago. Tomorrow, it's another day and we will see what happens."
Awaiting in the last four is second seed and wildcard Gael Monfils, who needed just over 90 minutes to see off Simone Bolelli 6-3 7-6 (7-4).