Now de Minaur may have to beat both American Taylor Fritz and Russian Daniil Medvedev to finish in the top two in the Ilie Nastase Group and qualify for the semi-finals.

Fritz had earlier on Sunday defeated a raging Medvedev 6-4 6-3 on one of the Russian's crazier days.

Yet de Minaur still fancies he can get through. 

"I always rate my chances. The way I see it is that Jannik was the only player in the group who I hadn't had a win against," the Australian said. 

"The rest of the players I've had some success against. Now I'm not playing the No.1 in the world anymore, I'll be looking forward to that.”

And so he should because Sinner is just an awful match-up for de Minaur. As if he's playing a super-charged, power-packed version of himself, he's now lost 15 sets in a row to the Italian.

Apart from a brief spell early when he earned a break to go up 2-1 and the Italian looked rusty after a four-week break, there was a brutal air of inevitability about the outcome.

“I knew I had my work cut out," admitted de Minaur. 

"I thought I started well, then I kind of slipped away. I just couldn't sustain the level that I needed.

“His ball speed, in my eyes, is so much higher than basically the rest of the people. From both sides he's solid. He keeps on improving. He's improved his serve so much throughout the years."

Just as at this time last year when Sinner swept the Australian aside in the Davis Cup final, once he'd cranked up that familiar easy power, he broke straight back and reeled off four straight games.

The world No.8 battled gamely at the start of the second set, cheered on at courtside by lollipop-sucking compatriots Jordan Thompson and Max Purcell, who had earlier on Sunday won their first match at the Finals doubles event.

Yet Sinner made his move in the fifth game, earning three break points and, after a medical emergency in the packed arena delayed proceedings for five minutes, he returned to complete the decisive breakthrough.

He ended up sweeping to victory, finishing the job with an ace down the T after one hour and 24 minutes, having crashed 19 winners to de Minaur's seven.

Compared to the first match it all felt positively ho-hum, because in the Fritz-Medvedev contest, the Russian completely lost the plot, serving three doubles in a row, smashing a racquet, threatening to make a return with a racquet handle and eventually getting docked a point.

Fritz didn't let the histrionics bother him. 

“I was just laughing. I think he’s really funny, to be honest,” the American said.

“Even when he’s not playing me, he always cracks me up."

De Minaur will doubtless hope the self-imploding version of Medvedev reappears against him on Tuesday.

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