The away win makes it eight of eight in the league for the Broomfield side and they are still in the hunt for promotion this season.
However, they were made to work hard for the win by a stuffy Bishopton side who had a powerful set of forwards intent on disrupting Cumnock's ball at all opportunities.
Cumnock struck first just minutes into the game when they won a penalty after a series of strong carries by the forwards in midfield. paul miller eased the ball between the posts to open the scoring.
The lead was short lived though and the home stand-off equalised with a penalty of their own.
Cumnock were looking sharp though and were quickly again on the attack. Pressure defence led to Bishopton conceding a scrum five metres from their line and stand-off Scott Houston drew a man before offloading to the supporting Jayson McMillan who was left with an easy finish.
Perhaps it was a lack of match sharpness – Cumnock have only played one game since November – but they went to sleep after this and let their hosts back into the game.
Some slack tackling allowed Bishopton to punch holes in Cumnock's defence and they were able to create an overlap out wide which they finished off. The conversion was added to give them the lead.
Cumnock were not playing like the side who had won every game so far and they were put under pressure due to some sloppy mistakes. There were bright sparks with Martin Thomson making a jinking run from full back deep into Bishopton territory and returning centre Martin Wilson carrying the ball aggressively.
It looked like all the good work was to be in vain though when prop mark linden was shown a red card for an altercation with the Bishopton scrum-half who was also shown a yellow for the incident.
Cumnock were dealt a double blow when David Kerr was sent to the sin bin for what was judged to be a late tackle on the Bishopton stand-off.
This set back seemed to spur Cumnock on to playing better, with replacement Blair McMillan setting the tone by chasing down everything that moved in a green jersey.
Cumnock regained the lead just after half time when Miller confidently hit his second penalty to give his team a one point advantage.
With Kerr back on Cumnock looked to be in a better position but then Jayson McMillan suffered a temporary loss of reason after being penalised for holding on in a tackle and his protestations with the referee led to the red card being produced again.
Again though playing with thirteen men seemed to inspire Cumnock to play better and spurred on by captain Campbell Reid they mounted a gutsy defensive effort, with half-backs Houston and Berrett making sure their team were playing in the right areas of the pitch with some clever kicks.
Cumnock wide men Wilson, Jason Robb and Gregor McMillan showed a willingness to chase everything, keeping Bishopton pinned back inside their own half.
The forwards also kept the scrum anchored through Kevin Brady and Sean Fulton, giving Cumnock a chance to attack again.
Both Houston and Graham Montgomery were held up over the line but eventually with time up Graham Hunter drove over supported by the pack to extend Cumnock's lead and seal what could be be a crucial victory.
After the match Cumnock coach Stevie Miller said: “The first half performance was simply unacceptable but the second was one of the most spirited displays I have ever seen by a Cumnock team.
“I am really proud of everyone on the pitch and the boys who were on the bench but didn't get on because the support showed real team spirit.”
Man of the match was Campbell Reid for his inspiring efforts as captain.

Team: Montgomery, Miller, Linden, Fulton, Hodge, M.Thomson, Kerr, Reid, Berrett, Houston, G.McMillan, J.McMillan, Wilson, Robb, M.Thomson.
Subs: Brady, McCrorie, B.McMillan, McGeary, Hamilton, Gilbert, McGuinness, Hunter.