Serena Williams -- Hits Rock Bottom in Miami!

Serena Williams made a complete ass of herself in Florida ... in a beautiful way.

The ridiculously fit tennis legend managed to safely pour all of her luscious buxom lady parts into an industrial strength black and white bikini in Miami on Monday.

With her champion badonkadonk workin' overtime, no one was injured when the bootylicious 31-year-old got high and waisted for a photo shoot on the beach.