The roof was half-closed on Arthur Ashe to shield the players from stifling temperatures amid energy-sapping humidity at Flushing Meadows.
American Fritz has been red hot all fortnight, not dropping a single set on his way to the last-16 stage, but he was ruthlessly extinguished by the 23-time Grand slam champion.
A demoralised Fritz has now lost all eight matches he has played against Djokovic.
The ninth seed hit more winners – 33 to Djokovic’s 25 – but he was simply ground down by the 36-year-old with a grand total of 51 unforced errors telling its own story.
He also forced 12 break points but converted only two of them, the second of which levelled the third set at 4-4 and prompted Djokovic to shoo some of his own supporters out of one of the executive suites.
But Djokovic immediately hit back, the three-time winner then saving another break point before completing the victory in two hours and 35 minutes to silence a partisan American crowd.
Djokovic said: “It’s expected that people are backing the home player, there’s nothing wrong with that. I like the atmosphere here, I’m fine with that and I thrive on that energy.
“I’ve been playing on this court for many years, played many epic matches, and I’m looking forward to another one in a few days.
“It’s a huge opportunity every time I step out on the court and at my age I don’t know how many more opportunities I’ll get.”