The home side knew a point would be enough to take the top spot in Group H. Third-placed Thistle came into the match needing to win by a 3 goal deficit to have any hope of qualifying.
Both teams started with a point to prove after last season’s fixture saw a series of errors gift St Mirren a 4-1 victory in the same fixture.
The first real action of the match saw the home side awarded a penalty in the 25th minute.
Driving down the right-wing, Jay Henderson was caught by the trailing leg of Richard Foster leaving referee Alan Muir no option but to point to the spot.
In the midst of transfer speculation, Midfielder Jamie McGrath stepped up with no doubt, sending Harry Stone the wrong way to give the Saints a deserved lead.
Thistle had a chance of their own soon after. A neat through ball into the path of Brian Graham gave him the opportunity to use quick feet, forcing an effort towards goal, however, he was denied by a great save from Jack Alnwick.
On the stroke of half time Alnwick was called into action again. An audacious effort from Stuart Bannigan left the Englishman scrambling to produce a strong save, keeping his clean sheet intact preventing the dipping effort.
The first chance of the second half came soon after the whistle. Jamie McGrath failed to stay composed smashing over the Jags bar from the resulting rebound of his first strike.
The home side continued to dominate proceedings as young Henderson continued to drive at the Jags defence, causing problems on numerous occasions.
St Mirren had the chance to double their lead just minutes from time. A dangerous cross from the right met Curtis Main free at the back post but he failed to capitalise, miraculously missing the target from yards out.
The match was wrapped up in the final minute of added time. A quick transition in the Thistle box saw the ball squared into the path of Captain Joe Shaughnessy leaving him the opportunity to finish into an empty net.
The extra goal made all the difference as St Mirren went into the 2nd round draw as one of the seeded teams, avoiding the top 6. Thistle bout out of this year’s competition after falling just short with the home side facing a trip to Livingston in the next round.
Man Of The Match – Jay Henderson
Still just 19 years of age, the tricky right back caused the Jags backline problems all day long, eventually leading to the penalty being awarded in the first half. Normally a left back, Goodwin was full of praise for the youngster who slotted into a position he has played very few times throughout his career with ease. Henderson looks an impressive prospect for the Saints and with the same level of drive and effort as today he could be a main player at St Mirren Park this season.