2015 US Open Celebrity Sightings - Day 10
Credit: Uri Schanker/GC Images

Before Justin Timberlake and Jimmy Fallon performed the History of Rap part 6 on The Tonight Show last night, the besties showed off their dance moves at the U.S. Open.

While watching Roger Federer defeat Richard Gasquet in the quarterfinals, Beyoncé's "Single Ladies" played over the loud speakers at the Arthur Ashe Stadium. Never ones to let a good dancing opportunity pass them by, Fallon and Timberlake stood up and grooved to the song with Beyonce's signature choreography.

Needless to say it was awesome, but the fun didn't stop there—watch the latest History of Rap below.