On a night were lower league teams smelt Premiership blood, the Jags suffered their own scare against Cowdenbeath but emerged unscathed, if a little traumatised, from their 3-1 League Cup ordeal.
It may have taken until extra- time for Alan Archibald's side to finally emerge victorious, but the top-flight newcomers eventually saw off Colin Cameron's team at Firhill as goals from Christie Elliot and Steven Lawless and an Aaron Muirhead penalty booked their place in the third-round draw.
It was far from Thistle's most accomplished showing on Archibald's watch, but as their Premiership counterparts toiled across the country it was a case of job done for the Firhill side.
Having become accustomed to the glamour of top flight football, this was a night for Archibald's side to dig deep. There were few glimpses of the free-flowing football that has won them many admirers so far this season, with passes going astray and moves too often breaking down.
The Jags saw plenty of the ball but weren't clinical enough in the final third, John Baird seeing efforts from Stephen O'Donnell crosses saved easily by Grant Adam and go wide of his right hand post. Two long-range efforts from Ross Forbes were also comfortably dealt with by the Cowdenbeath keeper.
The groans from the Firhill crowd told their own story, but they would have been significantly louder were it not for Scott Fox as the Jags No.1 prevented his side from going behind on 56 minutes.
Greg Stewart saw his jinking run come to an abrupt end courtesy of a Muirhead challenge, but Jamie Stevenson couldn't take advantage, Fox diving to his right to tip the midfielder's penalty to safety as the fans breathed a sigh of relief.
Thistle continued to toil, Baird trying his luck with another couple of efforts, but the breakthrough still evaded them - Archibald turning to subs Lawless and then Kris Doolan for inspiration as they searched for the opening goal.
Extra-time arrived and started with a bang as Archibald's final throw of the dice, Christie Elliott, gave Jags the lead within seconds.
After waiting 90 minutes for a goal, two arrived in quick succession as Kane Hemmings netted an immediate equaliser.
By now there was an urgency to Thistle's play as they swarmed forward in search of another goal and it was Lawless who came up trumps as he fired across Adam in an almost carbon copy of Elliott's finish.
Victory was, belatedly, secured for Thistle five minutes from time as Muirhead sent Adam the wrong way from 12 yards to ensure Thistle would avoid becoming another big- name cup casualty.