He was given a glimmer of hope after Sinner battled illness in his last-16 clash, where he admitted he was “not there health-wise” and had been “a bit dizzy at times” in hot weather.
But the Italian showed no evidence of any problems on a much cooler quarter-final day.
“Yesterday was a very easy day. I played just half an hour, 40 minutes with my coaches,” Sinner said when asked about how he was feeling.
“Talking about general physical [condition], you know, I feel like, especially when you are young, you recover very fast.”
In front of a patriotic home crowd, he broke for a 3-1 lead after a draining 24-shot baseline rally.
The agile Sinner’s big ball-striking proved hard for the Australian to counter and De Minaur struggled to create chances, managing just four winners in the opening set.
The second set followed a similar pattern with Sinner bossing De Minaur and breaking immediately to take control.
He was on a mission and a forehand winner earned him another break on his way to the second set in 40 minutes, with the Australian shaking his head in disbelief.
De Minaur tried everything but had no answers, broken twice in set three after a series of errors as Sinner powered home.
“Today I felt like I was feeling everything,” Sinner said.
“Days like this and you break quite early in each set, it’s a little bit easier.”
Sinner is bidding to defend a Grand Slam title for the first time after beating Daniil Medvedev in the final last year. He also won the US Open last year.
‘Boo me’
Shelton, a year younger at 22, will await him on Friday.
“Obviously he is one of the best servers on tour, a lefty ... so hopefully I’m ready, hopefully I can return as many serves as possible and then try to stay very concentrated about my game, like today, stay aggressive,” said Sinner.
The American demonstrated his potential by reaching his first semifinal at the US Open in 2023, where he was beaten by eventual champion Djokovic.
The left-hander came through a tough encounter with Sonego dominated by booming serves.
One monstrous ace sent down by Shelton clocked at 232km/h (144mph), the joint-fastest serve of the tournament.
He said afterwards that he wasn’t worried about who he played next.
“If it is the home favourite Alex de Minaur, then 100%, you can boo me, throw stuff at me. I understand,” Shelton told the crowd after his win.
“If it is the world No 1, probably the same thing, but I’ve got a few people in the crowd who will be pulling for me too.”
