Chris Paul: Kelly Kapowski Autograph Makes Him Geek Out -- She Was My 1st Love

Chris Paul musta been super jealous of Zack Morris as a kid ... because the NBA superstar was OBSESSED with Kelly Kapowski ... which is why he freaked out when she gave him a signed pic for his birthday last month.

Paul just revealed the gift -- a personalized autographed pic of Tiffani Thiessen that read, "Happy birthday my dear."

Paul said the pic was "easily one of the best Bday gifts I've ever received in my 29yrs on this Earth!!! #KellyKapowski #My1stLove #WeWereTogether #SheJustDidntKnowIt #CuzImSavedBytheBell"

After he posted the pic, another huge sports star chimed in -- Andy Roddick -- who wrote, "I'l literally am having issues containing my jealousy ... Back off CP!"

It's like Zack and Slater all over again.