The early stages were fairly even as Airdrie concentrated on keeping their back line intact and not allowing the more experienced Saints to pull them apart.
The visitors, for their part, seemed content to gently prod the Airdrie defence before in the latter stages of the first half really having a go.
Saints came closest to opening the scoring in 44 minutes when a Paul Sheerin header was well gathered on the line by Airdrie's keeper Mark McGeown.
Curiously, after the restart it was Airdrie who came back strongest, winning five corners in a ten-minute period as they turned the pressure on and forced Saints into a defensive role.
From those corners they created two genuine opportunities. Both fell to defender Scott Wilson who on both occasions sliced wide.
Falling on from that Owen Coyle linked well with David Dunn who despite being clean through on goal elected to pass rather than shoot when the latter option would almost undoubtedly have resulted in a goal.
However, in 85 minutes Airdrie broke the dead lock. Alan Gow's cross into the box was met by Jerome Vareille, whose left-foot shot gave keeper Kevin Cuthbert no chance.