Stephen Robinson's new look Saints suffered a demoralising 3-1 defeat in their final pre-season game before their Premier Sports Cup opener against Arbroath.
On the back of two strong wins in Northern Ireland Stephen Robinson set his side up in an attacking 4-3-3 formation against English League Two side Northampton, with Saints fans getting their first glimpse of summer signing Toyosi Olusanya who started on the right wing.
Ryan Flynn anchored the midfield alongside Mark O'Hara and Ethan Erhahon, with Charles Dunne partnering Declan Gallagher at centre back.
After a sluggish start St Mirren shocked the game into life as Marcus Fraser picked out Alex Greive on the edge of the box with a pinpoint cross.
The New Zealand international teed up Mark O'Hara who emphatically slammed into the bottom corner from 20 yards.
The Buddies' lead lasted less than ten minutes after the home defence came unstuck from a simple corner. Mitch Pinnock's delivery wasn't dealt with, Ben Fox eventually scrambling the ball in from close-range.
Saints striker Alex Greive was looking lively in an unfamiliar role on the left wing, regularly cutting inside to cause the Northampton defence a headache as he linked up with his fellow forwards.
Ryan Flynn and O'Hara dragged shots wide as the first half meandered to a close, with the intensity dropping dramatically after the visitors' equaliser.
St Mirren keeper Trevor Carson was called into action just before the break, denying Fox his second of the match with an excellent stop from the midfielder's long range effort.
The Buddies made two changes at the break, with Jay Henderson and Scott Tanser replacing Olusanya and Fraser respectively.
Carson had to be at his best again to deny Northampton, who fielded an entirely different XI in the second half, beating away Danny Hylton's header to keep the sides level.
Jonah Ayunga blazed over the bar from the edge of the box as both sides pressed for the lead.
Saints made six changes on the sixty minute mark, with Greg Kiltie, Dylan Reid, Kieran Offord, Peter Urminsky, Murray Campbell and Lewis Jamieson all entering the fray.
Offord drew a smart save from Jon Maxted as the Saints' young guns looked to spark the home side into life.
Saints sub keeper Urminsky then showcased his skill, pulling off an excellent low save to stop Josh Tomlinson's powerful low shot from nestling in the bottom corner.
St Mirren were desperate to bag a winner to send the home fans happy. It almost came when Offord swivelled cleverly on the edge of the box before flashing a vicious long range effort inches past the post.
With just over ten minutes to go Northampton finally found a decisive second goal. Some woeful defending from Saints' makeshift backline allowed Hylton to jab home from close range.
Things went from bad to worse for Robinson's side as Hylton made no mistake from the penalty spot to take the result away from the Buddies.
St Mirren: Carson (Urminsky 60), Fraser (Tanser 45), Gallagher (Shaughnessy 73), Dunne (Campbell 60), Tait, Flynn (Taylor 73), O'Hara (Kiltie 60), Erhahon (Reid 60), Olusanya (Henderson 45), Greive (Offord 60), Ayunga (Jamieson 60).
Subs not used: Strain.
