With Banbury Road still unfit, the decision to reverse the fixture proved justified and, despite difficult conditions, both sides must take credit for providing the 101 spectators with a great spectacle to start off 2016.
The early exchanges were aggressive but fair as both teams tried to assert themselves on the game.
The first real effort fell to the home team, with Ashley Gray putting his header well wide. A Harrison White effort also failed to trouble Matt Archer in the Southam goal as the Adders started to dictate play.
Southam, though, were creating chances of their own, Alex Andrews forcing Lloyd Storey into a smart save at his near post.
Player-manager Lee Constable then had a great chance to put his side ahead but his left-footed strike from the edge of the box was rushed and went over the bar.
In the 24th minute, Atherstone grabbed the advantage.
A misplaced backpass from Rob Sansom was intercepted by Liam Bailey who squared the ball to give Alan Miller an easy tap-in at the far post.
To their credit, Southam hit back straight from the restart.
Tunde Ajibade picked up Luke Wilson’s pinpoint pass and produced an excellent first touch to deceive the full-back before unleashing a shot from the edge of the area that gave Storey no chance in the home goal.
Saints started the second half sluggishly and invited unwanted pressure as they surrendered possession far too easily in midfield.
However, Archer was a relative bystander in the visitors’ goal and Saints slowly worked their way back into the game.
Jamie Simpson, 16, made his Saints debut from the bench just after the hour-mark and he made in immediate impact with a run and pass which saw Andrews denied by a last-ditch tackle from Mark Latham.
The match then swung on a decisive passage of play, with Storey denying Andrews in a one-on-one before Atherstone went straight up the other end and took the lead, Archer dropping a cross into the path of Liam Bailey who showed good composure to finish.
Another last-gasp tackle from the home side prevented Saints restoring parity, with Gray producing the vital intervention as Andrews prepared to pull the trigger.
With time running out, Layton-Hill found space on the left wing and his cross to the far post was met by Saints’ man-of-the-match Callum Ingram but unfortunately for Saints his header went just wide.
Saints entertain Heath Hayes on Saturday, while Racing Club Warwick, whose fixture at Coventry United was a victim of the weather, are at home to Stafford Town.