Janet Jackson and Tyler Perry have pulled off a big surprise at the U.s. box office - by beating a slew of big-name Hollywood projects to the top of the box office with a sleeper hit.

Tyler Perry's Why Did I Get Married? has rocketed to the top of the film charts with a stunning $21.5 million opening-weekend take, according to studio estimates.

The romantic comedy, which stars writer/director Perry, Jackson and singer Jill Scott was expected to open behind George Clooney's legal drama Michael Clayton, Cate Blanchett's Elizabeth sequel, Elizabeth: The Golden Age, and Joaquin Phoenix and Mark Wahlberg's crime thriller We Own the Night, but raced ahead of the competition.

Exact figures are still to be announced, but as Wenn went to press, last week's number one, The Game Plan, Michael Clayton and We Own the Night were all tied for second-place with just over $11 million.

Elizabeth: The Golden Age made just $6.2 million in its opening weekend.