Third seed Grigor Dimitrov progressed to the Australian Open second round with a straight-set win over Austrian qualifier Dennis Novak.
Dimitrov, 26, won 6-3 6-2 6-2 in one hour and 38 minutes on Rod Laver Arena.
"I just tried to be compact, focused, used every opportunity I had and tried to save some energy," said the Bulgarian, a semi-finalist last year.
There was a surprise exit for American 16th seed John Isner, who lost 6-4 3-6 6-3 6-3 to Australia's Matthew Ebden.
Canadian 18-year-old Denis Shapovalov reached the second round, seeing off Greece's Stefanos Tsitsipas 6-1 6-3 7-6 (7-5).