Sinner held aloft his arms in celebration after breaking Fritz to clinch the title and cheers rang around Arthur Ashe Stadium, even though home fans had hoped to see Fritz end a 21-year US men's Grand Slam drought.
Sinner was under a cloud of controversy at the start of the tournament after revelations that he tested positive twice for an anabolic agent in March but avoided a ban when an independent tribunal accepted his claim that the positive tests were the result of an unintentional contamination.
The top seed blocked out the furore in New York and with the win claimed his second Grand Slam title after winning the Australian Open earlier this year.
"We just went day-by-day, trying to practice well, even on the days off, believing in ourselves which is the most important. I understood, especially in this tournament, how important the mental part is in this sport," said Sinner.
"I would like to thank everyone for being so fair in this amazing arena. It was a huge pleasure."
Fritz got off to a dreadful start when he handed Sinner the break with an unforced error in the first game but settled his nerves, breaking back in the fourth game and surviving a 23-shot rally to save break point in the fifth.
But it was only a matter of time before the Italian would hit his stride and he broke the 12th seeded American with a perfectly placed drop shot in the seventh game. Fritz dropped his serve again on set point.
PILED MISERY
However, the momentum swung in Sinner’s direction as he broke Fritz on set point from the baseline and he piled further misery on the American when he clawed back from triple break point down in the opening game of the third set.
Fritz clung on and even went up a break but was left smacking his racket onto the court in frustration when he hit a volley into the net to let Sinner break back in the 10th.
Sinner broke for a sixth time in the contest to wrap up the win, with Fritz swiping a forehand into the net on match point.
"This title for me means so much because the last period of my career was really not easy," said Sinner, who climbed the stands to celebrate with his team as fans shouted "Bravo!" around him.
With US great Andre Agassi on court for the presentation ceremony, Fritz told the crowd: "I know we’ve been waiting for a champion for a long time so I’m sorry I couldn’t get it done this time.
"But I’m gonna keep working and hopefully I’ll get it the next time."
The win capped a blockbuster year for Sinner, who came back from two sets down to triumph at Melbourne Park and won in Miami and Cincinnati.
The world number one leaves New York with an impressive 55-5 win-loss record for the year, leaving rivals such as Novak Djokovic and Carlos Alcaraz in his wake.
"So many big wins for me this season, starting off with Australia and playing so well there which gave me confidence for until now," he said.
"But the work never stops. I know that I still can improve as we saw also today a couple of things but you have to be proud with what you have."
