Missed chances and sloppy defending consigned Southam to a sixth successive league defeat, writes David Hucker.
Saints found themselves a goal down after only two minutes when Ryan Harkin pounced on an error to put Copsewood ahead and never recovered from the early setback.
They should have equalised when Charlie Cook was clean through, but he placed his shot too close to keeper Dale O’Donnell and two follow-up efforts were cleared off the line.
Saints were forced into an early substitution when captain Tom O’Callaghan caught an elbow in the face which caused his eye to swell over.
The visitors increased their lead in the 35th minute when former Saint Connoll Farrell was given too much time and space to cut inside and shoot low past Matt Archer.
With four minutes of the half remaining, O’Donnell turned a Cook shot around the post and, from the resultant corner, Mike Harvey headed straight at the keeper with the net gaping.
Any chances of a second-half comeback were dashed in a seven-minute spell when Copeswood added three more through Daniel Fraser, Farrell and Reese Blackmore.
A late surge from the home side saw substitute Lewis Califano shoot just wide before Tunde Ajibade calmly slotted home a penalty to reduce the arrears.
In a final effort, a fine ball from Liam Cawley set up Califano, but his shot came back off the underside of the bar.
Saints are without a match tomorrow, but then face a tough trip to highflying Lichfield City next weekend.