Charlie Gilmour’s 33rd-minute strike put the Pars in control, though the hosts came roaring back after the break.

A disastrous moment for Billy Terrell gifted Logan Chalmers the equaliser and the goalkeeper was left red-faced again with 15 minutes remaining after he was caught out by Alex Samuel’s winner.

The Jags will now advance to face St Mirren over two legs for the chance to earn a place in the top flight for the first time since 2018.

Dunfermline were dealt a blow in the lead-up to kick-off following the news that Motherwell had exercised their recall clause for Aston Oxborough and the stopper was replaced by Terrell in the only change to Neil Lennon’s starting XI from the 1-1 draw in the first leg.

Thistle top scorer Samuel was preferred to Tony Watt in attack, while Robbie Crawford started ahead of Ts’oanelo Lets’osa.

The Pars showed intent right from the off, but a promising attack broke down when Callumn Morrison failed to make proper contact with his shot from just outside the box.

Terrell was worked for the first time midway through the first half when Ben Stanway could only direct his header from Chalmers’ cross straight into the arms of the away stopper.

It was an opportunity that seemed to jolt some life into the hosts. Dan O’Reilly glanced over from Aidan Fitzpatrick’s corner, prior to a snap-shot from Crawford that was easily claimed.

Dunfermline made the breakthrough with 12 minutes remaining in the first half after Gilmour capitalised on Ben McPherson’s poor clearing header by slamming the ball beyond Josh Clarke.

Fitzpatrick’s fizzing low delivery found no takers as the Jags looked for an instant response and it then took a good stop from Terrell to maintain the Pars’ lead after he sprung across his goal to keep out Oisin Smyth’s free-kick.

Partick boss Mark Wilson made a change at half-time, bringing on Watt for Crawford and he almost made an immediate impact.

However, the home side equalised after 50 minutes in calamitous fashion. Confusion between Alfons Amade and Terrell saw the keeper smash his clearance off the back of Samuel — and when the ball landed at the feet of Chalmers, he rolled it into the empty net.

After 63 minutes, Chalmers passed up a golden opportunity after firing wide following more excellent build-up play from Watt.

It required a vital headed block from Jeremiah Chilokoa-Mullen to keep out Chalmers’ rasping shot with 16 minutes remaining, but the Jags completed the turnaround one minute later.

Cammy Logan’s long pass caught out the Dunfermline backline and Samuel reacted quickest to head the ball over Terrell, who was left stranded after surging off his line.

The Scottish Cup finalists continued to fight to the end as Josh Cooper lashed the ball wildly over the top in the first minute of added time, but the hosts held firm to spark wild celebrations.