But to Mets fans, Yankees fans’ reaching across the aisle just shows them for the craven front-runners that they are.

“You can’t have it both ways,” Michael Flores said at the Playwright, invoking his sister, Priscilla Moronta, a Yankees fan who has rooted for the Mets since exactly last week. Mr. Flores, 34, who works in catering, produced his phone and waved a photo that his sister had posted to Facebook captioned, “Watching the Mets game with old friends.”

“Who are these old friends? From eighth grade?” he asked incredulously. “She can’t even name the pitching staff.” [Update: After publication, Ms. Moronta contacted The New York Times to assert that her brother was unequivocally mistaken.]

Some Mets fans said they detected a whiff of condescension.

“It’s kind of a younger-sibling relationship,” said Jesse Horowitz, watching the game at Union Grounds with Mr. Meyer. “ ‘Ahh, let the Mets have it one time.’ ”

He could have been talking about Officer Giunta. “There’s no reason for us to hate on the Mets,” he said, “because the Yankees are a better team in general.”

Or about Ashley Desch, a 21-year-old hostess at the Keg Room on West 36th Street in Manhattan. During the summer, Ms. Desch said, she would root so loudly for the Yankees that her downstairs neighbors in Astoria, Queens, would complain. But on Tuesday, clapping as Daniel Murphy, the Mets’ second baseman, hit yet another home run, she said, “I’m going for the next best thing.”

Also beware the motivations of Yankees fans in the hospitality business. “I have a vested interest in the bar being full, so I’m rooting for the Mets,” said the owner of Union Grounds, Tyler Maganzini, 35. “I want the Mets to go to the World Series. And I prefer that they then lose in seven games.”