The Glasgow team had narrowly won when the teams met recently at Cumnock and the Ayrshire side were determined to get a better result this time out.
They started brightly and despite a saturated playing surface were playing some fine attacking rugby and Jayson McMillan finished off an early break to touch down.
Cumnock were comfortably on top in the early stages but the wet conditions meant a lot of scrummaging, though the front row coped well with their opposite numbers,
Powerful carries by forwards James Gibbs and Joe Bennett gave Cumnock a good platform to play off and stand off Richard McGuinness made good use of it to step through the defence to score in the corner.
Cumnock then dozed off and a number of unforced errors allowed Cartha to get their hands on the ball and make ground. Good tackling kept the home side out for a while, with back row pair Martin Wallace and Andrew Watt well to the fore, but eventually Cartha found space out wide to squeeze over the line.
This spurred Cumnock back into life and they went close through captain for the day Andy McCrorie before the ball was shifted through the hands for Gregor McMillan to touch down just before half time.
Cumnock kept up the pressure in the second half with Stephen Taylor keeping the tempo high from scrum half and Kenny Barr repeatedly crossing the gain line in the midfield.
However, the deteriorating playing surface made running rugby difficult and neither team were able to make much of an impact.
Gregor McMillan showed his eye for a gap when a space opened up at the side of a ruck and the winger broke through unopposed for his second try.
Cartha then came back into the game and quickly closed the gap with a try straight from a number eight pick up, swiftly followed by another from short range.
Cumnock hit back again and reopened their lead with slick hands from the backs leaving Jason Robb just enough room to cross the line in the corner.
With just a point in the game, Cumnock set up camp in the Cartha 22 to try and make sure of the points. An attempt at a drop goal from Jayson McMillan came off the cross bar but a Cartha knock on gave Cumnock a good attacking position. Jamie Thomson picked and drove on before slipping an inside pass to David Kerr who dropped over from close range.
Cartha went in search of a try but to no avail and Cumnock were able to head back home with a vital bonus point win.

Next week: Cumnock 1XV play a crucial league clash with Bishopton at Broomfield while the 2XV take on Annan.