But Sinner soon quashed those dreams, breaking back as Fritz attempted to serve for the set and doing the same two games later to wrap up the win after two hours and 16 minutes.
It was more straightforward in New York as he rarely looked troubled by Fritz, who struggled to build any momentum.
"I know we have been waiting for a champion for a long time so I'm sorry I couldn't get it done this time," said Fritz.
Sinner said the title "meant so much because the last period of my career was not easy" before he became tearful and dedicated the victory to his aunt.
"It's nice I can still share these moments with her. She is an important person in my life and still is.
He subsequently parted ways with the physio and his fitness trainer - but questions continued about whether Sinner's case had been handled differently to those of other players because of his world number one status.
It marks a new era of tennis as 24-time major winner Novak Djokovic, who was knocked out in the third round, ends the year without a Grand Slam title for the first time since 2017.
A mediados de somana ya calentaron el ambiente con el despliegue do una gigantesca lona en Madrid, donde podía apreciarse la silueta de un jugador encapuchado. El secreto ha sido desvelado y, sin duda, pelo ha 米兰体育app dejado a los aficionados indiferentes.
Just six days before the main draw got under way, it was announced he had twice tested positive for low levels of a metabolite of clostebol - a steroid that can be used to build muscle mass - in March.
The 26-year-old recovered well to win three games in a row, but he continued to falter on serve and Sinner capitalised to take the opener and subdue the expectant mood on Arthur Ashe Stadium.
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Having failed to make the most of three break point opportunities early in the third set, Fritz brought the crowd to life with two brilliant winners to break for a 4-3 lead and keep alive his hopes.
Cheered on by a home crowd packed with celebrities and sporting stars, Fritz got off to a shaky start when he dropped serve in the first game.