Chris Erskine, pictured, scored twice and Stevie Lawless and Abdul Osman also found the net but if the Maryhill side had wanted to they may have won by twice the margin.
It was a clinically professional performance from Alan Archibald’s side and the Firhill manager had the added of bonus of the first appearance of the season of Mustapha Dumbuya, who tore his Achilles in the summer and played the second half.
Erskine gave them the lead in ten minutes when he latched on to Osman’s knock down from Sean Welsh’s free-kick and slotted a left-foot shot past Ewen MacDonald.
Then the Aberdeenshire side were effectively put to the sword in the space of 60 seconds.
At the end of an excellent passing move in 30 minutes, Lawless took a pass back from Welsh and drove a low left-foot shot into the right corner.
Formartine then contrived to lose a third goal straight from their own re-start when Paul Lawson lost possession and Kris Doolan seized on the opportunity to play in Erskine, who finished with some aplomb.
Formartine looked a better side in the second half but if it was not for Partick being over-elaborate in the last third, it would have been a more convincing win.
In the end, Thistle added only one more goal and it came in the 64th minute. Lawless played a good ball in from the right side and Osman diverted it into the right corner.
Manager Alan Archibald said: “We picked a side to go and do a professional job and they did that. It was great to get Dumbuya back. He still has a long way to go after being out for so long but he is like a new signing.”