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A day on from his utterly dominant 6-0 6-1 defeat of Casper Ruud, Sinner was completely out of sorts early on as  Paul raced to a 5-0 lead.

Despite pulling one game back, the Italian sat down a set behind, after failing to breech some sensational defending from the American.

But the slump ended there, and Sinner set about squaring the ledger in the second, and did so with the same strength and purpose that saw him past Ruud, serving up a bagel for Paul, who simply couldn't cope with a Sinner in top gear.

From 3-0 in the decider, Sinner was pegged back to 3-2 but broke Paul's serve again and sailed to victory from there on, completing his win in one hour and 44 minutes in front of an adoring home crowd.

"I just tried to stay there mentally," Sinner said.

"Today the conditions were different. It was much colder, heavier. I struggled with that a little bit and he broke me straight away. I tried to stay there, mentally what might work better. I stayed there in the first set. Winning the one game was very important. Tennis can change quickly.

"Today I showed that every moment is crucial and I am very happy about that and very happy to be in the final."

This was Sinner's 26th consecutive win, and he will face Carlos Alcaraz in the final, who beat another Italian in his semi-final, downing Lorenzo Musetti in straight sets.

Alcaraz is 6-4 up in the head-to-head with world No.1 Sinner, but will have to battle another partisan crowd and Sinner to further improve that record.

Sinner showed signs of injury through the second half of the deciding set, and explained the issue after the match.

"Since the third round I have had a small blister under my foot," he said on.

"It doesn't allow me that well to move in some moments. Today I felt it more than yesterday, and with the leg I am not concerned, it was just a bit tight, that is normal.

"I have to take care of this blister but there is no excuses. With the adrenaline there will be a lot of energy and for Sunday [Monday AEST] I am 100 per cent not concerned.

"If I want to win ... I need to play my best tennis for sure. Carlos played some incredible tennis today, so let's see what is coming. From my side, it is incredible to be in the final."