The world number one resigned after when he was a bishop down in the endgame against Polish grandmaster Jan-Krzysztof Duda, who is ranked a relatively humble number 15 in the world.
But on Saturday evening, 22-year-old Duda managed to do what no one — including the world's top 10 players — had managed to do since July 2018.
It was Duda's only win of the tournament in Stavanger so far and, as he told Chess 24 afterwards, “I didn't expect to win this game.”
But he was, he said “extremely happy, obviously”.
Carlsen, who is often tough on himself in post-game analysis, offered no excuses. “Extremely disappointing”, he said: “Completely unforgivable”.
Carlsen's undefeated run stretches all the way back to July 31, 2018, when Azerbaijani grandmaster Shakhriyar Mamedyarov defeated him. During that time, Carlsen scored 44 wins and 81 draws against his opponents.