The son of the 1998 Australian Open champion Petr Korda, the 31st-ranked American defeated the seventh seed 7-6 (9/7), 6-3, 7-6 (7/4) on Rod Laver Arena to advance quickly to the round of 16.
Korda’s shock set up a matchup with Hubert Hurkacz, the 10th seed from Poland, for a spot in the quarterfinals. Hurkacz defeated Denis Shapovalov of Canada 7-6 (7/3), 6-4, 1-6, 4-6, 6-3.
The 22-year-old Korda described the encounter as “an fantastic match,” saying that his game plan was to “just go for it” even if he was experiencing emotional ups and downs.
“I performed amazing, and I’m happy right now.”
Medvedev was a losing finalist at the last two Australian Opens, to Novak Djokovic in 2021 and then in a demoralising five-set defeat 12 months ago against Rafael Nadal after leading by two sets.
He was attempting to become only the fourth man in the Open era to reach three consecutive Melbourne Park finals after Djokovic, Mats Wilander and Ivan Lendl.
But that quest is now over as he joined defending champion Nadal, second seed Casper Ruud and eighth seed Taylor Fritz as high-profile first-week casualties at the season-opening Grand Slam.
Djokovic remains in the hunt for a 10th title, but has a hamstring injury and confessed on Thursday he was “worried” it could derail his tournament.
Korda displayed his credentials when he pushed Djokovic to the brink in the Adelaide International final this month, earning a championship point before the Serb rallied to win in three close sets.
The Florida native bounced back to claim a pair of victories in Melbourne against Cristian Garin and Yosuke Watanuki before meeting former world number one Medvedev.
Korda started aggressively, earning four break points in an 11-minute opening game before putting one away to take an early edge.
The Russian had minor treatment on his right hand at the changeover before Korda consolidated for 2-0.
The American dominated from the baseline in some lung-busting rallies and broke again for 4-1, before the Russian came roaring back with two breaks to level it up at 4-4.