Top seed Novak Djokovic and defending champion Stan Wawrinka posted contrasting straight-sets wins on Thursday, advancing to the third round of the Australian Open.

Djokovic defeated unseeded Russian Alex Kuznetsov 6-0 6-1 6-4 in one hour and 24 minutes on Rod Laver Arena.

The world No.1, bothered by a flu and stomach bug in the lead-up to the event, now meets Spanish 31st seed Fernando Verdasco or Japan’s Go Soeda.

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Defending champion Wawrinka needed two tiebreaks and over two hours to dismiss world No.194 Marius Copil in his second-round clash.

Wawrinka was expected to have a brief hit-out against the Belgian qualifier, but had to call on all of his class in the 7-6 (7-4) 7-6 (7-4) 6-3 victory on Margaret Court Arena.

Copil, playing his maiden grand slam, made a major impression with his powerful serve.

One was clocked at 242km/h, giving him the fastest to date in the tournament.

More importantly, Copil’s 17 aces gave fourth seed Wawrinka limited wriggle room.

The fourth seed only twice broke Copil’s serve in the match.

But Wawrinka’s experience in the tiebreaks was telling and the Swiss will continue his title defence against Finland’s Jarkko Nieminen in the third round.

Nieminen downed German Matthias Bachinger 7-6 (7-4) 7-5 7-5.

Fifth seed Kei Nishikori knuckled down after dropping his first set of the event, defeating Croatian Ivan Dodig 4-6 7-5 6-2 7-6 (7-0) on Hisense Arena in a match that lasted almost three hours.

Nishikori next faces American Steve Johnson, who posted an upset win over Colombian 30th seed Santiago Giraldo in straight sets.

Nishikori was twice broken in the opening set, but world No.86 Dodig couldn’t keep pace in searing heat.

Dodig saved one match point to hold serve and force a final tiebreak, but it was all in vain with Nishikori failing to drop another point.

Nishikori lost to Marin Cilic in the final of last year’s US Open and is seeking his maiden grand slam title.

In other early men’s results on Thursday, 19th seed John Isner beat Andreas Haider-Maurer 6-4 7-6 (7-4) 4-6 6-4.

Adrian Mannarino retired due to heat exhaustion, handing victory to 12th seed Feliciano Lopez.

– AAP