World number one Novak Djokovic was in dominant form in a 6-3 6-2 6-2 victory over American qualifier Mitchell Krueger.
Krueger broke the Djokovic serve to lead 2-1 in the opening set but from there battled manfully to keep things competitive, eventually falling to defeat in two hours and three minutes.
Djokovic will next face France's Jo-Wilfried Tsonga in a rematch of the 2008 final.
Zverev seals comfortable win
Alexander Zverev answered doubts about his fitness with a comfortable win over Aljaz Bedene in the first round of the Australian Open.
The fourth seed finished last season on a real high by beating Roger Federer and Novak Djokovic back to back to win his biggest title at the ATP Finals but arrived in Melbourne nursing a hamstring injury and then rolled an ankle in practice.
He was briefly a break down in the opening set against Bedene, back representing his native Slovenia after a spell competing for Britain, but from then on was barely troubled in a 6-4 6-1 6-4 victory.
Kyrgios fails again
Nick Kyrgios will tumble further down the rankings after losing in the opening round to Milos Raonic.
The Australian paid for dropping outside the top 50 by drawing 16th seed Raonic and is now likely to be around 70 when the standings are updated following a 6-4 7-6 (5) 6-4 loss.
Kyrgios received treatment to his right knee throughout the match and made no secret of his irritation at another injury problem with some colourful language.
Nishikori and Hyeon win in five sets
Eighth seed Kei Nishikori looked to be in major trouble against qualifier Kamil Majchrzak when he lost the opening two sets but the Pole was stricken by cramp early in the third set and eventually called it a day trailing 3-6 6-7 (6/8) 6-0 6-2 3-0.
Last year's semi-finalist Chung Hyeon, the 24th seed, also staged an impressive comeback, recovering from two sets down to defeat Bradley Klahn 6-7 (5/7) 6-7 (5/7) 6-3 6-2 6-4.
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