American Sebastian Korda defeated former world number one Daniil Medvedev 7-6 (7), 6-3, 7-6 (4) for his biggest triumph.
The 22-year-old son of 1998 Australian Open champion Petr attacked the Russian 2021 US Open champion with 50 winners and several net charges.
Korda exclaimed, “Probably one of my best bouts.”
“Just kept going after it. I stay optimistic. Never give up.”
On Rod Laver Arena, the 22-year-old fired wins from both sides, mixed it up with serve-volley, and lofted some lovely drop shots.
The 29th seed won the first set in an 85-minute tiebreak and the second in one break.
Medvedev showed his brilliance at a break down in the third, but Korda won the tiebreak again to set up a match against 10th seed Hubert Hurkacz.