John Mayer performed a smashing, impromptu show at Village Underground in the early hours of yesterday morning. Owner Noam Dworman told us Mayer’s comedian pal James Smith came in at 2 a.m. “and said John Mayer wanted to do a show at 3 a.m., and would tweet if we agreed. We were already closing down, and we had to call all the staff back. He tweeted it, and within 60 minutes the place was packed with 200 people. Alone on guitar, Mayer did about two masterful hours, mixing music and very funny banter. The crowd ate out of his hand and had the time of their lives. To see one of the great artists of our era in such an intimate setting was clearly a thrill for everyone.” Dworman added, “At the end at 5:15 a.m., John refused to take any of the money collected at the door and asked that it be given to the waitresses and bartenders, which made them very happy.” Mayer, who’d started the night at CV, ended it by singing “Billie Jean” with a man on West Third Street.