Roger Federer has shaken off a strong challenge from Bulgaria’s Grigor Dimitrov and his lingering illness to move into the Brisbane International’s final four.

Still battling the flu that has hampered his Australian Open preparations, defending champion Federer was occasionally off-colour but ultimately prevailed 6-4 6-7 (7-4) 6-4 in the quarter-final clash at Pat Rafter Arena on Friday night.

The win sets up a semi-final clash with Austrian up-and-comer Dominic Thiem while the man he beat in last year’s final, Milos Raonic, takes on Bernard Tomic in the other semi on Saturday.