Gilles Muller beat second-seeded Pablo Cuevas 7-6 (5), 6-4 on Thursday to advance to the Sydney International semifinals against two-time defending champion Viktor Troicki.
Troicki was scheduled to face No. 5 Philipp Kohlschreiber in another quarterfinal Thursday, but the German player withdrew with a back injury, handing third-seeded Troicki a walkover into the last four.
Troicki is attempting to become the first player in the Open era to win three consecutive Sydney titles.
Cuevas saved six set points during the first set, including two in the tiebreaker. In the second set, Muller broke Cuevas' service for a 4-3 lead and was never threatened for the remainder of the match.
In later women's semifinals at Sydney, second-seeded Agnieszka Radwanska was scheduled to play Barbora Strycova and, in a night match, Johanna Konta was taking on Eugenie Bouchard.
At the WTA's Hobart International, Elise Mertens had an upset 6-2, 7-5 quarterfinal win over top-seeded Kiki Bertens.
Jana Fett beat Veronica Cepede Royg6-1, 6-4 to reach the semifinals.