Bottom side Shannon fell to their eighth defeat in nine Ulster Bank League games as Clontarf took the spoils at Coonagh on Saturday afternoon.
Boosted by their recent improved displays, it looked as if Shannon's revival might continue when they went 9-3 ahead midway through the first half.
Place-kicking scrum half Rob Guerin put them in front with a well-struck early penalty and Leinster's Noel Reid, who lined out at full-back, levelled for 'Tarf soon after.
But indiscipline in the heavy conditions gave Guerin two more shots at the posts which he gratefully accepted in windy conditions.
The match took a turn in Clontarf's favour though when Shannon openside flanker John Shine was yellow carded.
While he was off, a hole was punched in the home defence and Clontarf winger Michael McGrath swept through for the first try of the year at this level at Coonagh.
Reid converted and he also added the extras to McGrath's second touchdown as he took his tally for the league campaign to five tries.
Shannon kept in contention thanks to a try before the break from lock Emmet McLoughlin, which left the Limerick men just 17-14 in arrears.
McLoughlin squeezed over after a strong set of phases from the Shannon forwards who got their rolling maul going and chipped away further with pick and go drives.
However, the only score of a turgid second half was a Clontarf penalty from Reid as the north Dubliners, who remain in fifth place, claimed their first league win of 2013.
The losing bonus point was Shannon's only reward for another typically committed performance with the likes of captain Tadhg Bennett and number 8 Paddy Butler standing out.
Credit to Clontarf's defence, they held the Limerick outfit at bay when they came under pressure in the final quarter with Killian Lett, Mark Flanagan and Martin Garvey all having big games.
Referee: Dudley Phillips (IRFU)