Alexei Popyrin has got his Miami Open campaign off to a winning start after his opponent Mikael Ymer retired at 1-0 down and 4-4 in the second set.
Popyrin, the sole Australian winner across the ATP 1000 Masters event and the WTA tournament on Wednesday, had taken the opening set 7-6 (7-5) before his Swedish rival pulled up with an ankle injury.
The world No.93 will face No.26 seed Botic van de Zandschulp of the Netherlands in the next round.
His fellow countryman Aleksandar Vukic was unable to keep his qualifying form going, losing to Serbia's Laslo Djere 6-2 7-6 (7-3), while in the women's first round Storm Hunter fell 6-0 7-6 (7-5) to the 2020 Australian Open champion Sofia Kenin.
Four more Aussies will be in action in the round of 128 after Chris O'Connell and Thanasi Kokkinakis, who both lost their final qualifying round matches on Wednesday, were promoted into the main draw after several late withdrawals.
There they will join world No.70 Jason Kubler and qualifier Jordan Thompson.
Kokkinakis has been drawn against Belgian wild card Zizou Bergs, O'Connell faces French veteran Richard Gasquet, Kubler takes on Brazil's world No.81 Thiago Monteiro, and Thompson will be up against Slovakia's Alex Molcan.
World No.18 Alex de Minaur will get his Miami campaign underway in the second round.
With seven competitors reaching the first round, this is Australia's highest representation in a Miami Open men's singles draw since 2001.
Elsewhere in the men's first round, Serbia's Dusan Lajovic survived a 16-shot rally on the final point to beat Andy Murray 6-4 7-5 and set-up a meeting with Maxime Cressy of the US.
It was disappointing for three-time grand slam champion Murray, who reached the final in Doha last month.
The 35-year-old flung his racket in frustration after a costly unforced error - one of 15 across the match - late on and told reporters he had expected a better performance.
"I served pretty well, but the rest of the game was a bit of a problem today," he said.
"I didn't really return that well (and) made a number of errors that I wouldn't expect to be making."
- with Reuters
