Viktor Troicki
Viktor Troicki of Serbia hits a return against Milos Raonic of Canada during a men's singles match at the China Open tennis tournament in Beijing, China, October 5, 2015. Reuters/Kim Kyung-Hoon

Defending champion Viktor Troicki, Bernard Tomic, and Grigor Dimitrov are through to the quarterfinals of the 2016 Apia International Sydney after winning their respective second-round matches on Wednesday.

Troicki ousted Tommy Robredo, 6-1 6-4 in the Sydney event to book a quarterfinal meeting with qualifier Nicolas Mahut, who earlier upset fifth seed Andreas Seppi in three sets, 6-3 1-6 6-3.

Tomic, a former champion and runner-up, beat Aussie wild card Jordan Thompson in their first meeting on professional tour, 6-2 6-2. Tomic, who fired six aces, dispatched his compatriot in 49 minutes. Troicki looms a potential semifinal opponent for Tomic.

Fourth seed Dimitrov, who is coming off from quarterfinals defeat to Roger Federer in Brisbane, also progressed to the last eight. The Haskovo native eliminated unseeded Pablo Cuevas, 7-6(2) 6-4. He will play eighth seed Alexandr Dolgopolov next for a place in the semifinals. Dolgopolov beat qualifier Alexander Sarkissian, 7-6(6) 6-2 on Wednesday’s second-round action in the men’s singles event.

Austrian rising tennis star Dominic Thiem is the highest seeded player eliminated in Sydney. The number two seed was forced to retire during the second set of his match against Giller Muller, 7-6(2) 2-2.

Men’s singles Round 2 results (Jan. 13, 2016)

Bernard Tomic def. Jordan Thompson 6-2 6-2

Teymuraz Gabashvili def. Federico Delbonis 6-3 6-3

Vicktor Troicki def. Tommy Robredo 6-1 6-4

Nicolas Mahut def. Andreas Seppi 6-3 1-6 6-3

Alexandr Dolgopolov def. Alexander Sarkissian 7-6(6) 6-2

Grigor Dimitrov def. Pablo Cuevas 7-6(2) 6-4

Jeremy Chardy def. James Duckworth 7-6(5) 6-4

Gilles Muller def. Dominic Thiem 7-6(2) 2-2 (Retired)

Day 5 Schedule (Jan. 14, 2016)

Alexandr Dolgopolov vs. Grigor Dimitrov - Not before 2 p.m at Ken Rosewall Arena

Bernard Tomic vs. Teymuraz Gabashvili - Not before 6 p.m. on Ken Rosewall Arena

Jeremy Chardy vs. Gilles Muller - Not before 2 p.m. on Show Court 1

Viktor Troicki vs. Nicolas Mahut - Not before 5 p.m. on Show Court 1