Usher is proving to a gusher at the box office for "Chicago."

The long-running musical revival, which will celebrate its 10th anniversary on Broadway in November, spurted in ticket sales since the rhythm and blues superstar went into the show Aug. 22 to play shady lawyer Billy Flynn.

For Usher's first week in the musical (the week ending Aug. 27), the net gross for "Chicago," was $747,331, the League of American Theatres and Producers said Monday, jumping more than $240,000 from the previous week. Without subtractions for such items as credit card deductions and group-sales commissions, the figure was slightly higher — $808,652, Pete Sanders, a spokesman for the show, said.

And the advance ticket sales are strong, too, with the show taking in nearly $200,000 the Wednesday after Usher's opening, and more than $150,000 for each of the two days after that. The rush for tickets prompted producer Barry Weissler to keep the box office open until 11 p.m. through last Friday.

And, according to Sanders, Weissler has hired extra security to control the crowds that have gathered at the Ambassador stage door after each performance. Usher will star in "Chicago" through Oct. 1, but is in discussion to extend his contract for several more weeks.

Another pop superstar, Ashlee Simpson reportedly will play Roxie Hart, the murderous chorine at the center of "Chicago," in the London production of the Fosse-Kander and Ebb musical. According to the tabloid magazine Star, the performer began rehearsals for the show Monday in New York and will join the production at London's Cambridge Theatre sometime in October.

Sanders would not confirm the report and declined to elaborate.