Leinster Senior Cup final/ Clontarf 23 St Mary's 16: The momentum changed as constantly as the weather at the RDS yesterday but in the end it was the contribution of winger Niall O'Brien that was central to Clontarf's victory over St Mary's in the Leddin Finance Leinster Senior Cup Final.

O'Brien was at the centre of the two decisive moments of the game. He made the break in the first half that led to Clontarf's opening try when they were trailing after a slow start. And then after the interval he crossed the line himself just when St Mary's seemed on the verge of a comeback.

In truth, the pendulum swung in Clontarf's favour just past the half-hour mark when, with St Mary's leading 6-3, O'Brien made a dramatic burst from midfield that took him into the opponents' 22.

After withstanding a number of challenges he released to Niall Carson, whose pass was collected by centre Marc Hewitt, who touched down in the corner.

Prior to that it was St Mary's who had the better of exchanges after starting promisingly, albeit with the benefit of the wind.

After a period of sustained pressure they took the lead courtesy of a 12th-minute penalty from outhalf Jonathan Sexton.

And while fullback Darragh O'Shea levelled matters for Clontarf six minutes later, some good mauling from the St Mary's pack forced a 23rd-minute penalty, which Sexton confidently knocked between the posts.

It was the last time they would lead the game.

Hewitt's try put Clontarf ahead at the break and early in the second half they looked to be in control when prop Robert Sweeney emerged from a ruck to cross the line for a try which O'Shea converted to extend the advantage to 15-6.

St Mary's bounced back in the 52nd minute when a break from winger James Norton resulted in a try for centre Keith Douglas, which reduced the deficit to two points after Sexton kicked the conversion.

However, any hopes of an unlikely turnaround were put to bed almost immediately when the influential O'Brien raced onto his own kick to grab the try that put Clontarf out of sight.

Both sides added a penalty to their tally in the scrappy closing stages.

ST MARY'S: Lynn; Norton, Douglas, McWeeney (capt), Smyth; Sexton, Kilbride; O'Beirne, Duggan, Collins; Keane, Duggan; Nash, Gervais, Copeland. Replacements: Lewis for Smyth (half-time), Potts for Gervais (half-time), Lynch for Lewis (50 mins), McCormack for Duggan (52 mins), Donnellan for Keane (62 mins).

CLONTARF: O'Shea; N O'Brien, Hewitt, O'Donnell, Keane; P O'Brien, O'Loughlin; Wickham, Carson, Sweeney; Trenier, Wood; Quinn, D O'Brien, Ellison. Replacements: Purdue for Trenier (18 mins), Jackman for Carson (52 minutes), Dorian and O'Donnell for Wickham and Sweeney (65 mins), Downey for O'Donnell (68 mins), Geraghty and Woods for O'Loughlin and P O'Brien (78 mins).