Bieber fever was in full effect late Sunday night when Justin Bieber released his long-awaited new single, "Boyfriend."

Teasing fans with a countdown to the midnight release on Twitter, the 18-year-old posted a behind-the-scenes video before writing, "IM HERE. #BOYFRIENDonITUNES NOW!!! #BieberBlast," along with a link to purchase the single on iTunes.

Since the midnight release, reaction has been pouring from Bieber's devoted fans and music critics, with some comparing "Boyfriend" to Justin Timberlake (think "Justified," Timberlake's first solo album).

"Oh Bieber! Justin Timberlake called and wants his old N'SYNC b-side back," wrote @AskKatybook on Twitter.

"Bieber's new song #boyfriend is sick!!! Very Justin Timberlake-y," wrote @alexhalbert.

The comparison is a valid (and probably flattering) one. In "Boyfriend," Bieber slowly raps/talks, in a mature manner, delivering lines like, "Swag, swag, swag on you / chillin' by the fire why we eatin' fondue / I dunno about me but I know about you / so say hello to falsetto in three, two."

And falsetto he goes, in a very Timberlake fashion.

Overnight, the song has already reached the number one spot on the iTunes singles chart, as pointed out by Bieber himself on Twitter.

"WHAT?!?! #1 on ITUNES!!! haha. I LOVE U PEOPLE!! Thank u!! NOw let's keep it there and go for our first BILLBOARD #1!! this is nuts! #BLESSED," he wrote Monday morning.

"Boyfriend" is the first single off of Bieber's much-anticipated third studio album, "Believe." The album will be a follow-up to the extremely successful Christmas album, "Under the Mistletoe," which has sold more than 1.2 million copies in less than six months.

So does Bieber really sound like Timberlake on "Boyfriend?" Scroll down to have a listen yourself (audio courtesy of "On Air with Ryan Seacrest" and Island Records).

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