Isner, the highest seeded American in the draw, defeated Monfils 7-5, 6-2, 4-6, 7-6 (7/4) to reach the third round in a match which finished just before midnight on Thursday on a packed Louis Armstrong Court.
But the majority of the spectators got behind the Frenchman, who served up his trademark repertoire of leaps, bounces, flashy razor-sharp groundstrokes and smiling one-liners with the crowd.
By contrast, Isner was all business, never managing more than a discreet fist-pump to accompany a winner as the crowd opted preferred chants of "Monfils, Monfils" rather than "Isner, Isner."
"He's a fun-loving guy and an exciting guy to watch no matter where he is playing, but honestly it was a bit surprising," said Isner, the 13th seed.
"I know the New York fans. They like to see long matches and fifth sets, but I was a little disappointed. Not going to sugar-coat it. If I was playing him in France, it certainly wouldn't be like that," he said.
He added: "I didn't want to get involved in a hit-and-giggle match. I just wanted to stay focused. I didn't want to be too friendly out there."


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