While much was made of Slovenian international Robert Koren's midweek hat-trick against Newcastle, Moss regards midfielder Mooy as the man who makes City hum.
"He was very unlucky to miss out on the Socceroos and he's a player that makes them tick," Moss said.
"We have to make sure we are on our game defensively to nullify their strengths and I certainly believe there's some key areas that we can cause them problems as well."
His Melbourne City counterpart John van't Schip said Mooy is his "most stable and most important player."
"He can score, he can set up and his working attitude is really good and we're very happy he's playing for us," Van't Schip said.
The eighth-placed Mariners, who are seven points behind City having played one game more, have gone 12 games without a win going into Sunday's clash.
A loss to surging City, who has taken 10 points from its last four games could do severe damage to the Mariners playoff prospects.
"I've said to our boys it's an absolutely crucial game," Moss told AAP on Saturday. "We're at home and we need to start winning games, it's as simple as that.
"The performances have been improving and we're looking a lot more threatening now when we go forward than we were earlier in the season."
For the second straight round City will go into the game with a longer rest period than its opponent, each of whom have had to back up after just three days.
"There's two teams going into battle tomorrow, one that has had two extra days recovery, it's an un-level playing field," Moss said.
"That's the cards we were dealt and we'll just get on with it."
While satisfied with the Mariners' effort against Western Sydney in the New Yar's Day goalless draw, Moss is contemplating making changes to freshen up the side.
One newcomer, who might get a run is striker Travis Major, who the Mariners have picked up from NSW National Premier League club, Blacktown City.
While City seems to be hitting its straps, Van't Schip isn't underestimating the task of beating a team that hasn't won since the opening round of the season.
"We have a difficult game coming up against Central Coast," he said.