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 with a recurrence of a back problem.

Federer, a nine-time winner of the tournament, 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.