WANTAGH, N.Y. — “Here’s to Billy Joel — that’s why we’ve got a gig,” Mike DelGuidice called out from his piano at Mulcahy’s, a pub and concert hall here on Long Island. As he and his band, Big Shot, performed covers of songs like “My Life” and “Scenes From an Italian Restaurant” on a recent Friday night, a regular crowd of revelers occasionally stopped taking selfies long enough to applaud, or at least clink their beer bottles in appreciation.

Running a tribute band, as Mr. DelGuidice has done for nearly 15 years, can be occasionally unglamorous work, but it has provided invaluable training for his other vocation: playing Billy Joel’s music, alongside Mr. Joel himself, as the newest member of his band.

Just a week earlier, Mr. DelGuidice was one of a few musicians onstage in the otherwise empty Nassau Coliseum in Hempstead, N.Y., practicing with Mr. Joel as that best-selling singer-songwriter prepared for his New Year’s Eve concert at Barclays Center in Brooklyn. At 42, Mr. DelGuidice (pronounced del-JU-das) has a rugged, tattooed exterior and a shaved head that belie a gentle demeanor.

While the mischievous Mr. Joel, running the rehearsal from his own piano, raced through impromptu renditions of Cream’s “Tales of Brave Ulysses” and “The Godfather” theme, Mr. DelGuidice matched him chord for chord on a guitar, never losing the tempo or the grateful smile on his face.