Only fourth seed Andrea Petkovic and Julia Goerges had won titles out of the last eight competitors at the International clay-court event but, both fell to defeat.
Petkovic started well against Monica Puig and had chances to break serve in the sixth game of the match, but failed to convert and allowed her Puerto Rican opponent to capitalise.
Puig maintained her momentum in the second set and secured the first semi-final appearance of her fledging career with a 6-4 6-4 victory.
Goerges battled hard in her quarter-final with Madison Keys in Strasbourg but after levelling the match at one-set all she was unable to complete the win, and Keys ran out 6-2 2-6 6-2 victor to set up a last four clash with Puig.
The second semi-final will see Christina McHale face Spaniard Silvia Soler-Espinosa as they continue to dream of a maiden title.
Soler-Espinosa had to come from a set behind in her match with Camila Giorgi to record a 3-6 6-4 7-5 win, and McHale was handed her place when opponent Zarina Diyas retired through injury with the American 6-2 3-1 up.