The American 12th seed arrived in Australia having never beaten a top-10 opponent at a Grand Slam and sealed a memorable victory with a clinical performance to equal his best result at a major.
Fritz, a quarter-finalist at last year's US Open and Wimbledon in 2022, sent down 13 aces and 50 winners as Tsitsipas's frustration mounted, and closed out the contest in just over three hours with a backhand winner.
"I was just really trusting my shots," the 26-year-old said in his on-court interview. "I served well the whole match. It just kept me in it and then when I really needed it at the end I just started playing my best tennis."
Fritz's victory came at a cost for his girlfriend Morgan Riddle, who had promised her social media followers she would eat an entire jar of Vegemite on Instagram Live if he won the match.
"My girlfriend thought I was too confident to win the match," Fritz added when he was handed a jar of the Aussie food spread by his on-court interviewer.
"This is a big jar but a bet's a bet. I have tried it, but I'm not the biggest fan so I won't be partaking, but I'll make sure it happens."
