IN the dressing room of an Atlantic City nightclub, furnished by the request of its current occupant with cheese steaks from the White House Sub Shop and a full array of Tastykake snacks, Jerry Seinfeld was explaining the stand-up comedy ritual of “getting in the bubble”: a state of mind that a performer seeks before show time, a few final moments of calm before the tumult of an unpredictable live audience.

And make no mistake. When Mr. Seinfeld faces his crowd, he is usually thinking of the exchange in raw, physical terms: a competition to be won or lost. “I want to get ’em bad,” he said.

Minutes later he emerged from the bubble and onto a stage at Resorts Atlantic City, to riff about the banalities of bachelorhood and marriage, Cinnabons and iPhones, burials and cremations, and relentlessly to mock an indiscreet heckler who had made the mistake of announcing that his nickname was Potato Head.

The hourlong routine was a crucial opportunity for Mr. Seinfeld to practice his act at a time when he feels, as he often does, that he’s not performing enough. “No matter how many times you’ve done it in the past, it’s got to be polished or it goes away,” he had said backstage. “The act just packs up and starts walking away.”