Lappin scuffed his shot into the keeper's arms in the first half, whilst Ryan McCay and Alex Burke combined to set up McGinty in the second, but his shot was saved.
The Saints lineup was: Smith, Reid, Broadfoot, Brady, Potter, Maxwell, Molloy, Lappin, Burke, McGinty, Corcoran. The subs were: Baird, McKenna, Stephen Anderson and McCay.
Saints next game is against Morton on Saturday at Cappielow, assuming they win their Renfrewshire Cup semi final.