Ryan Lee scored the winning try seven minutes from time to earn Barnstaple a 17-13 win at Drybrook.
Victory keeps Barum top of the South West Premier for another week, although chasers Maidenhead are now level on points after their 43-42 win over the Cornish All Blacks.
Drybrook led for almost all of the game after taking an 11th minute lead when centre Ben Large charged over, but never far enough in front to feel anything other than anxious.
Two yellow cards three minutes apart in the latter stages of the game did Drybrook no favours either.
They were down to 13 men when Lee scooted over after good work in the build up by Josh Davies.
Winston James, the Barnstaple captain, said it was not a vintage performance but added he would take four points away from Pottington any day of the week.
"It was almost a replay of our game up there last season," said James.
"Drybrook played really well and caused us a lot of problems from start to finish.
"Even after we got ahead we had to hold on for the final nine or ten minutes, which was hard work.
"Unusually for us we did not keep the ball well through the phases. What we did do was play in the right areas of the field, which made it harder for Drybrook."
Barum trailed between the 11th and 21st minutes until Brendan Darley zipped in for a try, which Jake Murphy converted.
Two Tim Stephenson penalties either side of half time edged Drybrook 13-7 up.
James got a try back on 51 minutes, reducing the margin to 13-12, and it stayed a one-point game until Lee's late clincher.
Barnstaple welcome University of Exeter to Pottington Road this Saturday.