The long awaited on-screen union of Jackie Chan and Jet Li reaped rewards for Liosgate and The Weinsten Company as The Forbidden Kingdom leapt to number one thanks to an estimated $20.9m three-day gross.

The martial arts adventure takes place in modern-day America and a mythical past in China where a youngster learns how to defend himself and rescues a god in the process.

Chan and Li helped overall box office climb for the first time in a month as the top 12 releases combined for $82.1m, up $12% against the same weekend last year.

Universal's romantic comedy Forgetting Sarah Marshall, produced by Judd Apatow and starring Jason Segel, Kristen Bell, Mila Kunis and UK comic Russell Brand, opened in second place on $17.3m.

The critically lambasted thriller 88 Minutes with Al Pacino opened in fourth on $6.8m through the little used TriStar Pictures label while the education documentary Expelled: No Intelligence Allowed opened in ninth place on $3.2m.

Last weekend's champion Prom Night fell two places on $9.1m for $32.6m while Fox Searchlight's police drama Street Kings with Keanu Reeves dropped five places to seventh and stands at $19.9m after two weekends.

TWC staged a limited release for Morgan Spurlock's documentary Where In The World Is Osama Bin Laden' and the results weren't good. Spurlock's follow-up to 2004's hit Super Size Me grossed $143,200 from 102 sites.

Next weekend's wide releases are: Fox's thriller Deception with Ewan McGregor, Michelle Williams and Hugh Jackman; Universal's comedy Baby Mama starring Tina Fey and Amy Poehler; Warner Bros' comedy Harold & Kumar Escape From Guantanamo Bay with John Cho and Kal Penn; and MGM's drama Deal starring Burt Reynolds and Shannon Elizabeth.

Estimated Top 10 North America Apr 18-20, 2008
Film (Dist)/Int'l dist/Est wkd gross/Est total to date

1 (-) The Forbidden Kingdom (Lionsgate/TWC) TWC/Mandate
Int'l/Relativity $20.9m -
2 (-) Forgetting Sarah Marshall (Universal) UPI $17.3m -
3 (1) Prom Night (Screen Gems) SPRI $9.1m $32.6m
4 (-) 88 Minutes (Sony) Nu Image $6.8m -
5 (4) Nim's Island (Fox) Summit Entertainment $5.7m $32.9m
6 (3) 21 (Sony) SPRI $5.5m $69.9m
7 (2) Street Kings (Fox Searchlight) Fox Int'l/Regency $4m $19.9m
8 (6) Dr Seuss' Horton Hears a Who! (Fox) Fox Int'l $3.5m $144.4m
9 (-) Expelled: No Intelligence Allowed (Rocky Mountain Pictures) $3.2m -
10 (5) Leatherheads (Universal) UPI $3m $26.6m