The pals performed a fifth installment of their popular segment on Friday, as they closed out Fallon's inaugural week as host of The Tonight Show.
The 33-year-old entertainer and the 39-year-old late-night host unleashed some classic tunes, including a medley of verses from hit makers LL Cool J, Run DMC, Tone Loc, Beastie Boys, Kendrick Lamar, Salt-N-Pepa, Jay Z, DJ Jazzy Jeff & the Fresh Prince and much more.
Even though the "Suit and Tie" crooner had to cancel his concert on Wednesday, Timberlake showed no signs of feeling under the weather.
"Are you on Mucinex right now?" Fallon inquired.
"I did the Mucinex," Timberlake explained. "Now I'm on straight up hardcore things. We're not going full Rob Ford, but probably enough that you shouldn't be on national television," he quipped.
"You see, that's how edgy we are," Fallon said. "You don't know what's gonna happen."
Timberlake also brought back his unbelievable impression of Fallon, which he most recently performed during Saturday Night Live in December.
(E! and The Tonight Show starring Jimmy Fallon are both part of the NBCUniversal family.)