Julius Erving Says Aaron Gordon Should've Won Dunk Contest

Julius Erving's one of the GREATEST DUNKERS in the history of basketball ... and he tells TMZ Sports that Aaron Gordon deserved the dunk contest win!!

We talked to Dr. J -- who was in the building for the dunk contest -- at Reagan National Airport in Washington D.C. on Monday ... and we asked the hoops legend if the Orlando Magic star was robbed by the judges in Chi-town.

"I don't know if robbed is the right term, if it had ended in a tie, I don't think anybody would've been upset. But, a contest like that going into basically 2 overtimes. Third overtime. You hate to have a loser."

BUT, forced to pick a winner, Dr. J -- who won the inaugural ABA Dunk Contest in 1976 -- says Gordon's final dunk…