Willie McLaren had an early chance to give Airdrie the lead when he spun on a Bryan Prunty pass inside the box but he blasted his shot several feet wide of Chris Smith's goal.
Saints made him regret the miss in the sixth minute by taking the lead.
Stewart Kean played in John Sutton who burst powerfully into the box but his shot was blocked by Stephen Robertson. Unfortunately for the keeper, David van Zanten was following up and he planted the ball firmly into the unguarded net.
The home support settled back to await Saints' consolidation of their superiority but, only five minutes later, Airdrie equalised.
Prunty out paced John Potter as he chased a through ball into the box and Smith lacked conviction as he came off his line and only succeeded in knocking the pacey striker over. Stephen McKeown netted the penalty without difficulty.
The league leaders lost their assurance and Robertson was barely troubled for the remainder of the opening half, saving from Kean and being grateful for Neil McGowan's goalline clearance to deny van Zanten.
Just after the hour mark, Paul Lovering deflected a Hugh Murray drive over his own bar but Airdrie were reduced to 10 when Stephen Docherty was ordered off for foolishly elbowing Charlie Adam as the players formed a wall.
Despite frantic pressing, Saints could not pierce a resolute Airdrie defence and Robertson dealt capably with a late Sutton drive.