De Minaur takes on Sinner at Rod Laver Arena on Wednesday night having lost all nine previous encounters with the world No.1 and defending Open champion, dropping the past seven matches without even winning a set.
Australian strategist Craig O'Shannessy believes Sinner is more vulnerable right now - and not only because of the Italian's ill health.
Respected coach Craig O'Shannessy (left) believes Alex de Minaur can beat Jannik Sinner at the Open. (HANDOUT/CRAIG O'SHANNESSY)
O'Shannessy, who helped Novak Djokovic to four grand slam titles while working with the Serb from 2017 to 2019, has noticed a sharp improvement in de Minaur's attacking mindset and tactics.
"De Minaur's got a couple of things in his favour," O'Shannessy told AAP at Melbourne Park.
"Firstly, remember he got sick yesterday. I don't know what it was but he certainly got the jitters.
"Number two is that Demon is winning 56 per cent of his baseline points, which is higher than Sinner, who's at 55 per cent.
"It's close but a one per cent advantage from the baseline is a big deal.
"So I see more offence. He looks more potent from the back of the court, making opponents uncomfortable.
"He's rolling through the tournament with more confidence, and you just feel the tables have turned a bit.
"While Sinner was surging, it doesn't feel like Sinner is surging at the moment.
"But it feels like Demon is surging."
O'Shannessy is urging de Minaur to retain an attacking mindset against Sinner. (Lukas Coch/AAP PHOTOS)
What makes O'Shannessy's assessment and belief that de Minaur can spring a boilover even more telling is the fact the US-based coach and strategist has been one of the masterminds behind Italy's rise from the tennis doldrums to super powers and back-to-back Davis Cup champions.
The 58-year-old has been working for the Italian federation since 2016 and plotted the game plans for Sinner and others during the past two Davis Cup finals, including their 2023 victory over de Minaur's Australian team.
"With the way Sinner has been feeling, if he gets a gets a hot night, that would also help Demon," O'Shannessy said.
"Humid conditions more than anything, if it's not even hot, but if it's really humid, and he continues attacking, he has a chance.
"He's got to attack and that's what he's been doing well leading up to this match.
"So I think it does come down to baseline performance early in the point, but Demon is certainly peaking at the moment.
"Don't get me wrong, de Minaur is still the underdog in this match-up but there's a stronger feeling that he's more ready than he's ever been to take on the challenge."
A victory over Sinner would present de Minaur with a huge opportunity to make the Open final.
He would play the winner of Wednesday's other quarter-final between American world No.20 Ben Shelton and unseeded Italian Lorenzo Sonego.
In Wednesday's two women's quarter-finals, American world No.14 Madison Keys plays resurgent Ukrainian Elina Svitolina before US eighth seed Emma Navarro takes on Polish world No.2 Iga Swiatek.
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