The 33-year-old actress rocked her fit body in a black and white bikini while Warren matched her in white swimming trunks.
Alba will reprise her role as Nancy in the upcoming sequel Sin City: A Dame to Kill For. In a recently released clip of the film, the actress' character -- who has undergone a drastic personality change since the previous film -- is seen going a bit crazy over a pair of scissors.
A Dame to Kill For opens in theaters August 22.
Swim Week Miami Beach 2014 [PHOTOS]