Defending champion Roger Federer reached the semi-finals of the Halle grasscourt championships on Friday without appearing on court as quarter-final opponent Lu Yen-Huen of Taiwan withdrew through injury.
Lu, who had self-deprecatingly announced that he faced a mission impossible against the Swiss former world number one when he said: "If I'm 150% and he's 100% I think I'd still lose", pulled out with a recurrence of a back problem.
Federer, a six-tine winner of the tourament, now faces Japan's world number 12 Kei Nishikori, who beat American Steve Johnson 6-1, 7-6 (7/4), for a place in the final.
Earlier, Philipp Kohlschreiber fought his way into the semi-finals by edging past fellow-German Dustin Brown 6-4, 5-7, 7-6 (18/16).
Kohlschreiber, who was on the losing end of a five-set marathon against Britain's Andy Murray at the French Open, prevailed after an epic third set tie-break against world number 85 Brown.
The defeat was a bitter disappointment for Brown, who had knocked out world number one Rafael Nadal the previous day.
Kohlschreiber, the 2011 champion, now plays 69th-ranked Alejandro Falla for a place in the final after the Colombian overcame another German Peter Gojowczyk 7-6 (7/4), 7-6 (7/2).
Wildcard Gojowczyk also saw his run come to an end in frustrating fashion, having claimed the scalp of third seed Milos Raonic of Canada in the previous round.