Maria Sharapova -- SLAMS Serena Williams ... Now It's Personal!

Maria Sharapova's rivalry with Serena Williams has left the tennis court and gotten SUPER personal ... and today Sharapova delivered an overhead smash about Serena's dating life for all the world to hear.

Serena fired the first shot in a Rolling Stone interview recently where she ripped on Sharapova (she didn't mention Maria by name, but the interviewer assumed it was her) by saying, "She’s still not going to be invited to the cool parties. And, hey, if she wants to be with the guy with a black heart -- go for it."

FYI -- Maria is dating one of Serena's rumored exes.

In a pre-Wimbledon press conference today, Sharapova took out her claws and got catty ... bringing up the fact that Serena is rumored to be dating her tennis coach (who is possibly still married).