Saints scrum-half Scott Moore kicked a late drop goal to give his side a narrow victory in their friendly at Knowsley Road. Moore's score gave Saints their first lead of the match and sealed the win against the Super League newcomers.
Leigh had the better of the opening exchanges with two tries from winger Rob Smyth.
But Saints rallied in the second half with Gareth Langley, Paul Anderson and Mike Bennett all going over.
Meanwhile, Warrington's Boxing Day derby clash with Widnes was postponed until 28th December (3:00pm) after the icy weather made the pitch unplayable.
Tickets bought for the clash are still valid for Tuesday's rearranged fixture.