Daniil Medvedev moved into the Australian Open second round with a straight-set victory over Switzerland’s Henri Laaksonen.
The US Open champion – the leading seed in the absence of Novak Djokovic – won 6-1 6-4 7-3 (7-3) at Melbourne Park.
Russian Medvedev was broken in the first game of the match but stormed through the opening set on his way to victory in just under two hours.
He will play Nick Kyrgios or British qualifier Liam Broady in round two.
Home favourite Kyrgios and Broady play in the night session from about 08:00 GMT on Tuesday.
Casper Ruud, the Norwegian eighth seed, pulled out with an ankle injury and has been replaced in the draw by lucky loser Roman Safiullin, who was beaten in qualifying by Broady.
John Isner, the 22nd seed, was beaten in a five-set match that lasted four hours 10 minutes, losing to fellow American Maxime Cressy 7-6 (7-2) 7-5 6-7 (4-7) 6-7 (4-7) 6-4.
Ugo Humbert was another seed to be eliminated on day two as the Frenchman, ranked 29th, fell to countryman Richard Gasquet 3-6 7-6 (7-4) 7-6 (7-3) 6-3.
Canada’s Felix Auger-Aliassime, the ninth seed, fought back from two sets to one down to triumph 6-4 0-6 3-6 6-3 6-4 against Finland’s Emil Ruusuvuori.
Roberto Bautista Agut and Grigor Dimitrov, the 15th and 26th seeds respectively, both needed four sets to see off Stefano Travaglia and Jiri Lehecka.
Elsewhere, Russia’s Andrey Rubev, Italy’s Jannick Sinner, Argentina’s Diego Schwartzman, American Taylor Fritz and Croatia’s Marin Cilic all won their matches in three sets.