Oops, she did it again: Spears is at number one
The 19-year-old's latest success makes her the first female solo act to reach number one with her first three albums.
Her new album, Britney, has sold just under 746,000 copies, according to SoundScan, an organisation that tracks retail sales in the US.
The figure is the second largest for the first week of any album released this year - only 'N Sync's Celebrity has fared better.
It also exceeds the combined sales figures for current albums by rival pop divas Jessica Simpson (513,000) and Mandy Moore (227,000) in their entire chart runs.
Spears has usurped Michael Jackson, the self-proclaimed King of Pop, in the number-one spot.
Jackson's Invincible - the star's first album of original music in six years - fell to number three.
The album sold 202,341 copies over the past week - down from 366,272 in its first week of release, a week ago.
Rock legend Pink Floyd's new compilation album, Echoes: Best of Pink Floyd, ranked number two, with 214,650 units.
Spears' triumph comes just weeks after she described her embarrassment at behaving like a "dork" when she met the woman who is, arguably, the most famous pop star in the world.
She said: "I'm usually so cool when I meet people, but once I was walking into the room I just felt something come over me and I was so nervous.
"So I walked in - I'm so embarrassed at what I said, I'm such a retard - and I said, 'I feel like I should hug you.'
"Afterwards I was like, 'Why did I say that?' She probably thinks I'm the biggest dork in the world."