Serena forehand destroys Rupert’s storefront window on ‘Letterman’ (VIDEO)

In town to defend her U.S. Open singles title (again), Serena Williams visited the "Late Show with David Letterman," where she had a friendly rally with the host Thursday before shattering beloved Rupert Jee’s Hello Deli window. 

Whatever those windows are made from — glass, Plexiglas — clearly they were not designed to withstand 80- to 90-ish mph bullets from a tennis pro. And she did it in heels, no less. 

Williams will face a human, Taylor Townsend, in the first round of the tournament. 

US Open ... mic — Serena shows off singing skills at New York club