"You're doing a really good job interviewing me, but I would like to interview me ... is there any way to do that?" the Australian actress asked Fallon when she appeared on the late-night show Monday.
"I have a way to make that happen!" he announced.
The competitive pair went on to swap mouths and compete over who can do the best accents such as Elvis Presley, a west coast surfer and even Blanchett herself.
They then sang a very creepy and slightly crooked duet of "Reunited" by R&B vocal duo Peaches & Herb.
Blanchett will next be seen in "Carol" playing an eponymous socialite who is trapped in a marriage of convenience while living in 1950's New York. But when she meets a young store clerk named Therese (Rooney Mara), the two form an immediate connection that threatens to tear their worlds apart.
"The Tonight Show" airs at 11:35 p.m. on NBC.
See more of our favorite Jimmy Fallon antics: