Clontarf proved best in the heavy conditions at Annacotty, running out 16-12 winners over hosts UL Bohemians. They were helped by a superb display by their former Leinster lock Ben Gissing who lorded it in the lineouts.
Only four points separated the sides at the interval with the north Dubliners just 10-6 ahead. Winger Michael Keating collected an early try, but Bernard Jackman's side had to regroup after the loss of out-half Noel Reid through injury.
He was replaced by former Ireland Under-21 international Martin Dufficy who had quite an influence on proceedings. He converted Keating's try and also landed three penalties - two of them in a hard-fought second half.
Keating crossed in the fourth minute, taking advantage of a defensive lapse from the hosts.
18-year-old out-half JJ Hanrahan got UL on the scoreboard, landing penalties after 15 and 23 minutes - the second coming on the back of some strong running from full-back Darren Moroney.
Dufficy kicked his first penalty, eight minutes before the break, to open up the gap again, before Hanrahan missed two late attempts at goal.
The place-kickers landed a brace apiece in the third quarter, Hanrahan's fourth penalty of the afternoon coming after 'Tarf lost their influential number 8 Simon Crawford to a yellow card.
The visitors, who defended stoutly in the closing stages, were able to absorb the pressure from UL who were short a number of their regulars.
Indeed, luck was not on their side on the day. Bohs lost Barry Murphy to a late Munster call-up, then his replacement Ross Butler injured his shoulder in the warm-up and team captain Martin McPhail was absent due to a flu bug.
Back rowers Kieran Essex and Tommy O'Donnell also sustained injuries at crucial stages during the game.
Referee: Richard Kerr (IRFU)