The competition, which took place on Thursday, involved Timberlake asking random questions about himself to see who knew him best.
Timberlake was unable to speak during his Tonight Show appearance, having to rely on cue cards to communicate. Timberlake is suffering from severely bruised vocal chords, which recently caused the pop star to delay an October concert in New York City to his birthday on Jan. 31.
Timberlake first asked his wife and close friend who his all-time favorite rapper is, explaining that the question had two answers. Biel won the round after correctly writing down Mase and Andre 3000 while Fallon failed by jotting down Run DMC.
Timberlake then asked what is his go-to cocktail, with Biel once again winning by answering tequila mule. Fallon was shocked that his answer of gin and tonic was incorrect.
"We drink gin and tonics! That's what we drink!" Fallon said. "You don't like what I do for you?"
Both Biel and Fallon correctly answered pineapple when asked what is Timberlake's safe word. Timberlake, for the final round, then asked what number he was thinking of between one and 5,000.
Fallon got the answer right by writing down 4,297, after Timberlake had helped him cheat. Biel then left The Tonight Show stage in disappointment with Fallon chasing after her.