Double defending champion Viktor Troicki eased into the quarter-finals of the Sydney International with a straight-sets win over Paolo Lorenzi on Wednesday.

Troicki has been victorious at this ATP 250 event in each of the last two years and, after enjoying a bye in the first round, had little trouble in seeing off the Italian 6-3 6-4.

One break in each set was all the Serbian needed, sealing victory with the first match point that came his way.

Troicki's 13th straight win at this tournament set up a last-eight meeting with fifth seed Philipp Kohlschreiber, who ousted home hope Jordan Thompson 7-5 6-4.

Top seed Dominic Thiem fought back from a set down to eventually overcome Gastao Elias 6-7 (5-7) 6-3 7-5 and set up a clash with Dan Evans, who was also forced to come from behind in defeating eighth seed Marcel Granollers 1-6 6-3 6-3.

The other two quarter-finals see Pablo Cuevas take on Gilles Muller, while Pablo Carreno-Busta will face Andrey Kuznetsov after their respective wins on Wednesday.

Meanwhile, at the ASB Classic in Auckland, there were a couple of withdrawals as defending champion Roberto Bautista Agut and his compatriot Feliciano Lopez bowed out.

Bautista Agut was struck down by a stomach virus, lucky loser Jose Statham failing to make the most of his second chance as 2015 champion Jiri Vesely won through 6-7 (6-8) 7-5 6-3 while a back problem forced Lopez to pull out and give Jeremy Chardy a walkover.

Like Vesely, Marcos Baghdatis fought back from a set behind to prevail 4-6 7-6 (7-4) 6-4 and two-time winner John Isner was also taken the distance against Malek Jaziri before coming through 6-3 3-6 7-6 (8-6).

Joao Sousa, Steve Johnson and last year's runner-up Jack Sock were the other men to book their quarter-final spots.