Harbury produced a big improvement on the previous week’s performance against Shipston with excellent ball handling and support play helping them edge out their derby rivals.
There was little between the two sides early on, with a penalty apiece getting both sides on the scoreboard.
Southam were the first to settle and a well-won lineout and several phases led to a try in the corner for Harry Hewson, converted by Lewis Dodds.
Harbury added another penalty before an opportunistic try from the visitors.
Southam had looked like scoring only for Pete Burnell to have the ball stripped from his grasp a metre from the line. Harbury countered but their attack was stopped in its tracks by a superb tackle by Sam Bench and winger Clark picked up the loose ball to streak away and score under the posts.
Harbury’s dominant pack then got their reward when the forwards rumbled to the line and Tom Kittendorf dotted down.
The successful conversion cut Southam’s lead to 17-13 at the interval.
Harbury started the second half with greater intensity and after a series of passes and excellent support play found themselves camped near Southam’s try line.
The hosts won another lineout and prop David Heydon drove over, with the extras giving Harbury a three-point lead.
Southam responded minutes later with their backs spreading it wide for Bench to score an unconverted try in the corner.
Harbury used their replacements well with centre Greg Swinburn and number eight John Wheelhouse blasting holes in the visitors’ defence.
With ten minutes remaining, the home side’s forwards laid the platform for their backs to work their way into the Southam 22.
Following a series of rucks, Southam were penalised and full-back Richard Mazurek struck the ball perfectly to take Harbury into a slender one-point lead.
Harbury’s superior power and fitness clearly showed in the final five minutes as they found themselves camped on the Southam line.
A scrum was awarded and Wheelhouse scored his first try for the club after the Harbury pack drove Southam over the line.
The conversion hit the post and rebounded to safety.