Rihanna vs. Karrueche Tran Instagram/Twitter War: Sexy Bikini PHOTO 'Wins' Chris Brown Back, 'The Monster' Tour Beauty Shares Racy Eminem Panties Pic

Rihanna's too busy heating things up onstage alongside Eminem to worry about the fact that ex-boyfriend Chris Brown's apparently back together with on-and-off again sweetheart, Karrueche Tran.

But it's no wonder why Breezy can't get enough of his former lovers. Both ladies are extremely sexy - and aren't afraid to flaunt it!

On August 17, both Tran and RiRi shared rather head-turning snapshots on Instagram and Twitter.

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The 26-year-old model donned her stunning body in a skimpy red-and-black bikini while partying in Las Vegas:

Meanwhile, "The Monster" tour beauty got a little more frisky...

@rihanna: "school. kills."

Yup - "role model" indeed! Notice that her tour-buddy's name is written right across the naughty "touching myself" pic ("Shady").

Looks like Tran and the 26-year-old songstress are in a viral social medial battle, and they don't even know it!

RiRi's racy snapshot already has more than 12,000 "likes" and counting, while Tran's less provocative photo's garnered 74,000+ fan "favorites." So, which beauty's winning?

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