Shortly after Alcaraz wove his magic to dismantle 24-time Grand Slam champion Novak Djokovic on Arthur Ashe Stadium, the usually machine-like Sinner misfired at times but prevailed to ensure a third successive major final with the Spaniard.
"I think five straight Grand Slam finals, it's something great. The consistency and putting myself there in the later stages of the biggest tournaments we have, it's amazing," said Sinner.
"I would have never thought that I would make this when I turned pro, and now I find myself here."
The Italian world No. 1 faced brief resistance in the fifth game of the contest but dialled up the intensity to hold and wrapped up the lopsided opening set when Auger-Aliassime sent a backhand wide.
Auger-Aliassime settled his nerves in his second New York semi-final, breaking for a 5-3 lead in the next set en route to levelling the match, before going toe-to-toe with Sinner in the third set, only for the momentum to shift again.
Sinner, who took a medical timeout for an unspecified issue earlier, found his groove to close out the third set and staved off a strong challenge from his reinvigorated Canadian opponent with some clutch serving in the next set to advance.
"Sunday is a very special day and an amazing final again," said Sinner. "I feel like our rivalry started here playing an amazing match. We are two different players now, with different confidence too."