Barnstaple dropped back from second to third in the South West Premier Division after they were beaten 16-7 by leaders Bournemouth.
Danny Southworth put Barum ahead with a seventh-minute try from a maul that Jake Murphy converted.
Bournemouth chipped away at the lead with a couple of penalties from Adam Davies, but remained a point behind at the break.
Joe Rees plunged over from a tap-go penalty just after the interval to put Bournemouth ahead. Davies converted.
Grant Hancox landed a last-minute penalty to deny Barum a losing bonus point.
Jeremy Chugg, Barnstaple’s chairman of rugby, said Bournemouth were deserved winners of a close game.
“They have a good side and were good value for their win,” said Chugg.
“We scored an early try from a 35-yard rolling maul, but it was a struggle to threaten them after that.
“Their half-backs were exceptional in awful conditions, but apart from them they have no real stars in the team.
“Bournemouth’s side is largely experienced players in the 28-33 age bracket – no youngsters – and they are good all round and all over the park.
“They put us under pressure and made us play from deep, which made it harder for us.”
Barnstaple were without forward Matt Gohl, who was under suspension having been ordered off in the 22-20 win over Old Patesians seven days earlier.
Barum’s own discipline committee banned Gohl for four weeks. The ban could be extended by league bosses if they feel it is too lenient.
Barnstaple have no game this Saturday afternoon. Their next outing is on Boxing Day afternoon when they face old foes Bideford at King George V in the traditional Christmas derby.