Taylor Fritz's upset win over Stefanos Tsitsipas at the Australian Open is one of the most important of his career - and he did not let his influencer girlfriend forget the bet they'd made beforehand.

Fritz stormed past last year's runner-up Stefanos Tsitsipas and into the Australian Open quarter-finals for the first time after beating the Greek seventh seed 7-6(3) 5-7 6-3 6-3 at Melbourne Park on Sunday.

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 U.S. 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.

Fritz's influencer girlfriend, Morgan Riddle, promised her 216,000 Instagram followers that she'd eat an entire jar of Vegemite if he won the match.

'If @taylor_fritz wins again ill eat a jar of vegemite on (Instagram) live,' she wrote.

Fortunately somebody had a jar on hand after Fritz won and brought it onto the court while he was being interviewed.

'My girlfriend thought I was too confident to win the match,' Fritz added when he was handed a jar.

'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.'

The tennis WAG gestured from the stands that she would prefer a much smaller jar than the one on offer. 

Morgan shot to fame during the Australian Open in 2022 after she posted a 'get ready with me' video that went viral on social media.

Since then, she has rebranded herself from a little-known WAG to an influencer and courtside fashion commentator, even hosting a series called Wimbledon Threads in 2023.

Morgan uses her social media pages to document private jet flights, beach holidays, city shopping trips, and courtside seats as she travels around the world supporting her sports star boyfriend.

Fritz will next play Serb superstar Novak Djokovic - a man he has never had a win against. 

'A lot of these match-ups were when I was a bit younger,' Fritz said.

'Since then I'm improved and (have) become a better player.

'The times I've played him since I haven't really brought my best level, and you need to if you're going to compete with someone like Novak.

'I feel confident. If I'm able to play like I did (against Tsitispas) then I'm a chance.'