By Peter Henderson

LOS ANGELES (Reuters) - Hapless martial arts hero Jackie Chan knocked amnesiac assassin Jason Bourne out of the top spot at the box office this weekend.

Together, the films are helping to propel the box office tally toward a record-breaking summer.

"Rush Hour 3," the buddy film starring Chan and Chris Tucker that comes six years after the duo's last romp, grossed $50.2 million in its first weekend at U.S. and Canadian theaters.

"The Bourne Ultimatum," the third installment of the espionage action series starring Matt Damon as a one-time CIA hit man searching for his past, took in $33.7 million in its second weekend playing in North American theaters, a 51 percent drop, according to studio estimates on Sunday.

Box office revenue since May 1 have hit $3.6 billion, compared with $3.3 billion last year, and this weekend was the fifth in a row to top year-ago numbers.

"This used to be called the dog days of August. Now the dog days are not so bad," said Media by Numbers chief Paul Dergarabedian, a movie business analyst. "We're looking really good for a record-breaking summer, something back in June we didn't think would be attainable," he said.

Animated feature "The Simpsons Movie" dropped 56 percent in its third weekend to $11.1 million, but pot-bellied anti-hero Homer Simpson finished ahead of two newcomers.

"Stardust," a fantasy film starring Claire Danes, grossed $9 million at No. 4 on the charts. That film's target audience includes older women who may not rush to theaters on opening weekend.

"Daddy Day Camp" took in $3.6 million and debuted at No. 10, reflecting strong competition from other family-oriented fare.

The long delay since the last "Rush Hour," was seen as a challenge for Tucker and Chan. "Rush Hour 2" set a record August opening of $67.4 million in 2001, which held until last week, when "The Bourne Ultimatum" took in $69.3 million.

"Rush Hour 3" was released by New Line Cinema, a unit of Time Warner Inc. "The Bourne Ultimatum" was released by Universal Pictures, a unit of General Electric Co.'s NBC Universal Inc.

"The Simpsons Movie" was released by 20th Century Fox, a unit of News Corp., "Daddy Day Camp" was released by TriStar Pictures, a unit of Sony Corp., while "Stardust" was released by Paramount Pictures, a unit of Viacom Inc.