Tristan Thompson did have sex with the woman saying he's her baby daddy, but it was years before she claims, years before her baby was born and long before he began dating Khloe Kardashian ... TMZ has learned.
Sources close to the NBA power forward tell us ... he had a one-night stand with the woman, Kimberly Alexander, sometime during his rookie season in 2011-2012. However, we're told this doesn't line up with her repeated claim he fathered her child ... because the kid in question is between 4 and 5.