After scooping the Australian Open, French Open and Wimbledon titles, Djokovic arrived in New York in pursuit of the full set, but a 6-4 6-4 6-4 defeat meant the calendar Grand Slam dream died.
Rod Laver, the last man to achieve that feat in singles, back in 1969, was in the crowd to witness what most anticipated would be a momentous moment in tennis history. Instead, it was momentous for Medvedev, the Russian finally a champion at the highest level.
It means Djokovic remains tied with Roger Federer and Rafael Nadal on 20 slam titles, the 34-year-old being served notice here that a new generation is rising, headed by world number two Medvedev.
It was a sizzling afternoon in New York, the temperature taking a leap a day on from Emma Raducanu's triumph in the women's final, and Djokovic was feeling the heat from the early moments.
Medvedev broke in the first game against a nervy and erratic opponent. Djokovic had said before stepping on court that he hoped to bring the "best version of myself" and promised he was "ready for the battle", but he was running on close to empty at times here.
Djokovic had dropped the opening set in the previous four rounds in this US Open run, winning three times in four sets and once in five during that sequence. He came into this match having spent five hours and 35 minutes longer on court than Medvedev, an unusually scenic route through the rounds for the top seed. And those extra miles in his legs showed, Medvedev swiftly a set ahead, sealing the opener with an ace.
Djokovic had won 10 of 10 matches in slams this year after losing the opening set. No man has ever won a slam after losing five first sets in the same tournament, the ATP said. That still holds true.
The Serbian had 0-40 on the Medvedev serve in the second game of the second set, but five points in a row from the man from Moscow felt like a bodyblow, and in the fourth game Djokovic's frustration spilled over, brutally smashing his racket three times against the ground.
Djokovic was landing only 50 per of first serves in court, and when he hit a feeble backhand into the net, Medvedev had two break points. He took the second of those when Djokovic looped a volley long, then held to love to lead 4-2.
On his third set point, Medvedev gave Djokovic a chance to make a passing shot, but the 34-year-old went wide. At two sets up, Medvedev may have had thoughts of Stefanos Tsitsipas losing from such a lead against Djokovic in the Roland Garros final, but this time Djokovic was fried.
He raced out to a double break and a 4-0 lead in the third set, yet double-faulted twice in succession when his first championship point arrived and gave back one of those breaks. Djokovic closed to 5-4, the New York crowd roared and the man who rarely feels loved by tennis crowds began to well up. Medvedev came out to serve again and again served a double on a championship point, but he had another in store and Djokovic netted on the backhand.
For the first time since 1990, when Pete Sampras and Gabriela Sabatini reigned over the rest, the US Open has a pair of first-time grand slam winners as its singles champion, with rookie Raducanu joined by the finished article in Medvedev.
In an extraordinary year for Djokovic, this was a lousy day.