The Australian international, who's thrived with the Scottish champions since returning from his impressive World Cup campaign, was involved in three of the goals for Ange Postecoglou's side in Sunday's early fixture in Perth's McDiarmid Park.
Not normally known for any prolific scoring feats from midfield, the 32-year-old has enjoyed a remarkably fruitful spell ever since his double against Hibernian at Easter Road on December 28.
And Mooy's confidence was in evidence from the moment his brilliant little through ball in the 13th minute initiated the opening goal that was to set Celtic on their way to the win that keeps them nine points ahead of Rangers at the top of the table.
His vision with the pass effectively left three defenders floundering and set up Kyogo Furuhashi to put in the low cross that the unfortunate Andy Considine, in his 600th club game, could only bundle past his own keeper.
A long, looping ball over the top from Mooy nine minutes later set Jota away down the right, and his cross went through the hapless Considine's legs, allowing Furuhashi to shoot home his 22nd goal of the season.
Though St Johnstone hit back with a thumping 25th minute shot from Drey Wright, it was Mooy who effectively killed off any hope of a comeback with a superbly dinked 37th minute goal.
Latching on to Jota's pass, he needed just a touch before artfully lobbing the ball over the advancing goalkeeper Remi Matthews to make it three.
With his side in total control, Mooy's distribution proved excellent in the second half too before his old Socceroos' boss Postecoglou took him off for a deserved rest 11 minutes from the end.
Poor old Considine's landmark day only got worse when he was sent off in added time for a pull on Oh Hyeon-gyu just outside the box, with Mooy's replacement David Turnbull then hammering home the fourth from the resulting free-kick.
It meant Postecoglou's side have now lost only once in 25 league games this season as they march towards back-to-back crowns under the Australian.
