She even had a dead-on impression of her lifelong frenemy
Aguilera, who returns to NBC's "The Voice" as a coach after sitting out the last two seasons, also had an amazing Cher and a decent Shakira.
While Aguilera costarred with Cher in the 2010 bomb "Burlesque," she has known Spears since the two were mere kids performing together on "The All-New Mickey Mouse Club."
While the pair have grown up together and each had their share of career highs and lows, Aguilera seemed able to tap into the Spears sound in a way only a close friend could.
And her assigned song choice was "This Little Piggy," which Aguilera perfectly adapted into the style of Spears "Hit Me Baby One More Time."
Meanwhile, Fallon did his best David Bowie and Michael McDonald impressions. But come on, we've all seen Fallon do better. The real attraction was Aguilera here, who landed another "moment" in the ongoing media narrative of the Aguilera-Spears friendship.
Here's hoping Brit-Brit took it all in stride. Maybe she'll appear on Fallon next with her best Aguilera impression.
We're all waiting.