Mitt Romney -- I Won't Fight Obama ... He Already Beat Me!

Mitt Romney wants NO PIECE of Barack Obama -- telling TMZ Sports he'd rather get in the ring with Evander Holyfield ... because he won't pick a fight he knows he can't win!

Romney and the "Real Deal" are all set to face off in a charity boxing match on May 15th in Utah to raise money for a charity that helps poverty-stricken people get blindness-reversing surgeries.

But when we asked if he'd go toe-to-toe with his presidential rival from 2012 -- Romney backed down ... saying, "I tried that. I didn't win. You may not have noticed."