Wildcard underdog Aleksandar Vukic has been unable to back up his maiden win at the Australian Open, losing to Moldovan Radu Albot in straight sets.
Vukic had his moments during Wednesday's second-round match at Melbourne Park, but could never capitalise against the world No.124, going down 6-4 7-6 (7-4) 6-4.
The 25-year-old missed opportunities to win the first two sets, but was forced to claw his way back from 1-4 down in the third.
Despite Vukic's brief comeback, where the right-hander broke serve for the only time in the contest, Albot was eventually able to close out the match in two hours and 16 minutes.
Vukic bows out from his home grand slam after last week reaching his first ATP Tour quarter-final in Adelaide.
Veteran John Millman is the second Australian man up on Wednesday, facing the giant task of tackling German No.3 seed Alexander Zverev on Rod Laver Arena.
The 32-year-old took down Spanish stalwart Feliciano Lopez in four sets on Monday to book a showdown with one of the tournament favourites.
It promises to be a big day of Australian action on Thursday, with Samantha Stosur stepping out for what could be her last singles appearance at Melbourne Park.
Stosur is playing in her 20th and final Australian Open and will enter her match against Russian No.10 seed Anastasia Pavlyuchenkova as a rank outsider.
AUSSIES IN ACTION ON DAY FOUR OF THE AUSTRALIAN OPEN
(PREFIX DENOTES SEEDING):
Men's singles, second round:
32-Alex De Minaur v Kamil Majchrzak (POL)
Nick Kyrgios v 2-Daniil Medvedev (RUS)
Chris O'Connell v 13-Diego Schwartzman (ARG)
Women's singles, second round:
Samantha Stosur v 10-Anastasia Pavlyuchenkova (RUS)
Maddison Inglis v Hailey Baptiste (USA)
