Roger Federer's conqueror Tommy Haas is out of the Mercedes Cup in Stuttgart after defeat to compatriot Mischa Zverev.
Hass, 39, handed his great friend Federer just a second defeat of the year on Wednesday, but could not follow it up as Zverev prevailed 6-4 6-4.
Third seed Thomas Berdych is also out after going down to fellow big server Feliciano Lopez 6-7 (4/7) 6-3 6-4, but fourth seed Lucas Pouille is through, beating Phillip Kohlschreiber 6-4 2-6 6-3.
Benoit Paire overcame Jerzy Jankowicz in straight sets 6-1 7-6 (7/4).
Top seed Marin Cilic is safely through to the last four of the Ricoh Open in s-Hertogenbosch.
The Croatian beat qualifier Vasek Pospisil in straight sets, triumphing 6-3 7-5.
In the semi-final he meets Ivo Karlovic, a 6-4 6-4 winner over Daniel Medvedev.
Alexander Zverev had little trouble in getting past Frenchman Julien Benneteau 6-0 6-4, while Gilles Muller got the better of British number four Aljaz Bedene 6-3 3-6 6-4.