Serena Williams , hubby Alexis Ohanian and Marc Anthony all rocked with Bruno Mars backstage before his concert in Miami last night ... but Serena's bod stole the show.
The tennis superstar just gave birth to baby Alexis a little over a month ago ... and she's already squeezin' into a skin-tight dress from gal pal Eva Longoria .
You could tell Serena and Alex were PUMPED to get some facetime with Bruno backstage ... and later during the show, jammin' to "Just the Way You Are" with Marc.