Justin Bieber "Believe" scores year's biggest debut so far

Singer Justin Bieber performs during the MuchMusic Video Awards in Toronto June 17, 2012.

LOS ANGELES (Reuters) - Canadian pop star Justin Bieber notched the year's biggest debut so far as his latest album, "Believe," sold 374,000 copies in its first week, according to figures from Nielsen SoundScan on Tuesday.

"Believe" will secure the 18-year-old singer his fourth No. 1 album on the Billboard 200 when the chart is officially published on Wednesday. It follows 2009's "My World," and 2011's "Never Say Never: The Remixes," and his holiday set, "Under The Mistletoe."

The new album knocked off last week's chart-topper, "Looking 4 Myself," by Bieber's mentor Usher.

"Believe" outsold Madonna's "MDNA," which debuted with 359,000 copies earlier this year. But it was unable to top the year's best sales week for an album, which went to Adele's "21," selling 730,000 copies in the week following her six Grammy Award wins in February.

Bieber embarked on a worldwide tour and filmed his first TV special to promote "Believe." But a TV special about the singer - "All Around The World" - aired over two nights on NBC last week, did worse than expected and pulled in less than 3.5 million viewers each night.

The full Billboard 200 album chart will be released on Wednesday.

(Reporting By Piya Sinha-Roy; Editing by Philip Barbara)