The top-seeded/world No. 1 Federer was tested by the fifth-seeded Davydenko in a hard-fought 6-4, 3-6, 7-6 (9-7), 7-6 (7-5) quarterfinal bout at Rod Laver Arena. Federer's semifinal opponent on Friday will be the 21st-seeded Kiefer.
In other play, Kiefer scored a 6-3, 0-6, 6-4, 6-7 (1-7), 8-6 victory over the 25th-seeded Grosjean in four hours and 48 minutes.
Kiefer won despite 67 unforced errors and 59 winners from Grosjean. Kiefer also had nine double faults and Grosjean had 12 aces to just four for his opponent.