Justin Bieber topped Billboard's "21 Under 21" list of the world's top young musical acts for the second year in a row, fending off stiff competition from British boy band One Direction.
Bieber, 18, "remains more powerful in the pop universe than ever," Billboard said, having released two No. 1 albums in the past year - holiday set Under the Mistletoe and his latest pop album, Believe.
One Direction, whose five members range in age from 18 to 20, burst onto the U.S. pop scene just six months ago after first soaring to success in their native Britain. Managed by British TV entrepreneur Simon Cowell, One Direction made history in March when it became the first U.K. group to debut at the top of the Billboard 200 chart with its first album.
Singer Demi Lovato, 20, came in third on the list.
