Canterbury never came to terms with a Devon mud bath as they sank to their ninth defeat of the season.
They were outplayed by a more direct Barnstaple side who mastered a testing surface with effective ball carrying and surer handling.
If there was any consolation for the city side it came from their second half defiance which restricted the home side to one try and denied them an extra bonus point.
Led by dynamic Number Eight Jarrard Hayler, the Barnstaple forwards controlled possession after the break, causing problems as they came on to the ball at pace and pinned the city side in their own half Canterbury, often static and lacking the essential physicality, looked ill equipped for a surface that deteriorated rapidly.
They were only six points behind at the half way point but their lack of bite in attack was already showing.
Barnstaple took an eight point lead in the first quarter through that rare sight these days, a drop goal from Gwyn Parks, and a try by Luke Berry.
That came after Aaron Cooper was yellow carded for a high tackle and the wingman got a second grab at the ball as a cross kick bounced in the in-goal area.
When the city side established attacking positions they could make little of them but on the half hour mark Dan Smart’s clever anticipation earned his side’s first and only points.
The fly half intercepted a pass to canter over between the posts and leave himself simple conversion.
In conditions where points were always hard to come by, Barnstaple then made the two scores that mattered.
In the final minute of the first half the City defence was too narrow, the Devon men found a gap and full back Jordan Petherbridge finished off with the try.
Three minutes after the break Canterbury gave away a penalty which Parks converted with a good kick from 44 metres out.
After that they were rarely seen as an attacking force as Barnstaple put on the squeeze and the pressure brought another, far more straightforward penalty for Parks.
They were still held back by a solid city defence but when Hayler broke from a wheeled scrum to send Will Topps over for their third try it really was game over.
Canterbury continued to defend bravely, their spirit epitomised by Harry Sayers brilliant try saving tackle which denied Barnstaple a bonus point, but they had little else to offer.
Canterbury: A.Moss, A.Miller (repl H.Sayers), J.Murray, C.Kingsman (repl O.Best), B.Howard, D.Smart, K.Braithwaite, A.Cooper (repl J.Green), T.Rogers (rel J.Otto), S.Kenny, J.Rigby, D.Bailey (repl A.Woodward), M.Cantwell.
Pictures supplied by Phillipa Hilton.