Maria Sharapova vs. Serena -- SWIMBLEDON ... Tennis Babes Bikini Rematch

Just one week after Serena crushed her on grass, Maria Sharapova took their epic rivalry to the sand ... and in this war, there are no losers.

Maria was spotted on the beach at Montenegro, flaunting her physique in a tiny maroon 2-piece.

Meanwhile, Serena Williams got her beach on too this weekend -- in a bikini that brings one word to mind ... ASS!!!

Rematch next week??