Bruno Mars may be Locked Out Of Heaven but he's locked in to the top of the U.S. pop charts, beginning the New Year as he exited 2012 - at number one.

The singer/songwriter has scored a fourth week atop the Billboard Hot 100 as Taylor Swift's I Knew You Were Trouble rises to two on the new countdown.

Rihanna's former number one Diamonds drops a spot to three, while The Lumineers' Ho Hey and Beauty And A Beat by Justin Bieber and Nicki Minaj round out the new top five.