The Italian legend pulled the strings as the Sky Blues beat the Mariners 1-0 thanks to Brett Emerton's late winner in the A-League on Thursday night and his performance did not go unnoticed by former Sheffield United midfielder Montgomery.
"The guy is world class, a magician, without any shadow of doubt," Montgomery told SBS.
"He is one of the world's greatest players and Sydney are very fortunate to him such a player in their ranks.
"Give him time on the ball and he'll punish you.
"He does not have to run around the pitch because when he gets the ball he comes alive. He can turn so quickly, even at his age.
"He has this ability of putting his body between the ball and the opponent and sometimes he is just impossible to mark.
"He is one of the best I have come up against and I've played 30-odd games in the Premier League.
"If Sydney play around him he will be a more outstanding player in the competition."