The hosts dominated the first half and took the lead through midfielder Paul Sheerin in the 32nd minute.
He was set up by Steven Milne inside the box after Queens keeper Barry John Corr had spilled an Andy Lawrie cross. Sheerin had a lot of work still to do with the finish but managed to lob it quite delightfully over a crowd of players into the top right hand corner.
Owen Coyle's Saints doubled their advantage with a great team move in the 38th minute. On-loan midfielder Paul Lawson provided the low driven finish from 35 yards for his first goal for the Saints.
Corr's nightmare continued in the second half when he missed a Milne cross, allowing the ball to find Sheerin, who produced a composed finish to claim his second of the match.
Queens' misery was compounded when Jim Thompson was sent off in the 74th minute for his second bookable offence.
The fourth goal came in the 78th minute from substitute Peter MacDonald, who fired home from close range after good work from Milne.
Milne himself completed the rout in the 80th minute, heading home from close range after Corr had parried a Simon Mensing header.