The only goal came early in the second half, striker Jack Smith slotting home to get the under-20s back to winning ways.
The game also saw Darren McGregor start as he continues his return from injury, with fellow first teamers Grant Adam and Jon Robertson also getting a run out. Missing was Thomas Reilly, who has been out injured for the last few months but is back in training. He has yet to feature for the second string since having his cast removed.
Saints are currently fourth in the table but have two games in hand over second placed Dundee United, who are four points better off.
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