LOS ANGELES/NEW YORK, Aug 17 (Reuters) - "Teenage Mutant Ninja Turtles," last weekend's most popular film, collected ticket sales of $28.4 million to top the U.S. and Canadian box office for a second consecutive week, beating "Guardians of the Galaxy" in a battle of superhero misfits.

"Guardians of the Galaxy" had ticket sales of $24.7 million at domestic theaters, according to estimates from tracking firm Rentrak.

"Let's Be Cops", an R-rated action comedy starring Jake Johnson and Daman Wayans Jr. pretending to be Los Angeles police officers, collected $17.7 million to open in third, ahead of action film "The Expendables 3," starring Sylvester Stallone and other action stars which took in $16.2 million.

"Teenage Mutant Ninja Turtles" is distributed by Paramount Pictures, a unit of Viacom Inc. Walt Disney Co released "Guardians of the Galaxy".

"The Expendables 3" is distributed by Lions Gate Entertainment Corp and "Let's Be Cops" by 20th Century Fox studio, a unit of 21st Century Fox.

(Reporting By Ronald Grover and Chris Michaud; editing by Jason Neely)