Holder Roger Federer scored a comfortable 6-3, 6-3 win over unseeded Spaniard Fernando Verdasco in the quarter-finals of the Hamburg Masters on Friday.
The Swiss world number one was joined in the semis by in-form Serbian Novak Djokovic, who brushed aside Verdasco's compatriot Albert Montanes 6-2, 6-3.
Federer took just under half an hour to wrap up the first set against Verdasco but had to beat back a determined challenge at the start of the second, saving several break points.
After holding his serve for a 3-2 lead, the 24-year-old Spaniard called for the doctor and had his right ankle heavily bandaged.
Federer took full advantage of his opponent's misfortune, breaking serve twice and cruising to victory in 81 minutes.
"He's a very talented player and he's got the game to upset anyone on any surface," the 12-times grand slam winner said at a news conference.
"In the end it was unfortunate for him that his foot hurt a little bit but I don't think that had much to do with it at the very end."
The Swiss, four times a winner in Hamburg, will meet Nicolas Kiefer of Germany or Italy's Andreas Seppi in Saturday's semi-final. The unseeded pair play later on Friday.
Second seed Rafael Nadal takes on fellow Mallorcan Carlos Moya in the day's remaining quarter, with the winner facing Djokovic on Saturday.
Currently number three in the world, Australian Open holder Djokovic will take over Nadal's number two spot if he does better than the French Open champion here.
The Serbian was far too good for Montanes on Friday, wrapping up the match in just 76 minutes.