the first time i tried this i did just a standard singles match for the tournament and it dident unlock for me after the game and then i had seen that doing it on a doubles match worked also, so i gave that a trie and it works great also its shorter then doing a tottal of 5 matches for singles and the doubles matches is just 3. Also if you get an AA ranking or higher for these doubles matches you can unlock the secret tournament stage against Doc eggman and Shadow. Also take into consideration if you r failing misserably trying to beat the final stage just press start and do retry and it will just reload the secret stage so you can keep trying.