Dom Joyce offered no excuses admitting his team only had themselves to blame after being hit with 12 penalty runs for a slow over rate allowing YMCA to edge a thriller by one-wicket against Merrion at Anglesea Road.
With the last wicket pair of Harry Tector and Padraic Flanagan at the crease 15 were needed off the last two overs before umpires Wood and Clarke intervened to award what were to prove a crucial 12 penalty runs.
Tector then crashed Tyrone Kane to the boundary through point to spark wild scenes of celebration among the Claremont Road faithful.
The Ireland Under 19 captain finished unbeaten on 64 from 79 balls (4 fours, 1 six) as YM chased what looked an above par target of 245 on a first-day of the season pitch which admittedly improved as the day progressed.
Simi Singh made an entertaining 41 while Sam Murphy and debutant Jarred Barnes both hit 21 - the latter striking two huge sixes in his 11-ball cameo.
It was however the double whammy of 41 wides which contributed to the slow-over rate which was to prove crucial in the final analysis.
Earlier South African born Barnes - who has Irish ambitions, hence his switch to Dubllin - was the pick of the YM attack, taking 3 for 37.
Merrion overcame a tricky opening period to make 245, thanks to partnerships of 90 for the 3rd wicket between Tyrone Kane (40) and John Anderson (34) and 79 for for the 6th between overseas player Poonish Mehta (47) and Michael Lewis (43*).
"That game had everything," YM skipper Jack Tector told Cricket Leinster. "The pitch wasn't tricky early on but improved through the course of the day and I felt their total was above par at the half-way stage.
"Our guys took the chasedeep and when you do that you always have a chance. I thought Harry played fantastically well and I had every faith that he and Flan (Padraic Flanagan) would get us over the line."
Merrion captain Dom Joyce offered no excuses admitting it was all their own fault for the penalty runs.
"We have only ourselves to blame," said Joyce. "We bowled 41 wides and that was the losing of the game.
"I thought we batted pretty well. I felt like it was a good total but didn't feel safe as it's a fast scoring ground and the boundaries are small.
"It's a pretty devastating loss. It's the first game of the season though and I think teams will all beat each other in a competitive league. We have a home game next week where I hope we will bounce back."
LEINSTER PREMIER LEAGUE
At Anglesea Road, Merrion lost to YMCA by 1 wicket
Merrion 245/6 (50 overs; Poonish Mehta 47, Michael Lewis 43*, Tyrone Kane 40, John Anderson 34; Jarred Barnes 3-37).
YMCA 247/9 (48.1 overs; Harry Tector 64*, Simi Singh 41, Sam Murphy 21, Jarred Barnes 21; Poonish Mehta 3-30, Tom Stanton 2-42, Sean Stanton 2-47).