Clontarf were denied a famous victory on Leeside right at the death as Darragh Lyons swept through for the match-winning score for Cork Constitution.
Brian Walsh's men trailed 17-3 early in the second half and were still five points in arrears in the closing stages of this entertaining, edge-of-the-seat seat Ulster Bank League opener.
But Darragh Lyons had the final say, the full-back showing a clean pair of heels to the cover to scoot over and level the game for a spirited Constitution side.
Team captain Gerry Hurley then added the match-winning conversion to give the Leesiders an early push in their bid to regain the league title.
Former Cork Con favourite Richie Lane had given Clontarf a 14th minute lead, using the wind to clip a 45-metre penalty through the uprights.
The hosts, now dominating possession, responded well but were unable to get off the mark with scrum half Hurley missing two penalty attempts.
Hurley succeeded at the third attempt, however 'Tarf got in for a try just before the break as hooker Cathal O'Flynn broke off the back of a well-organised maul to score.
Lane converted and also added the extras to an opportunist try from scrum half Dermot O'Meara, six minutes after the resumption.
O'Meara took a quick tap penalty and caught the Cork Con defence napping as he coasted in. The seven-pointer rewarded some hard grafting from likes of Ben Reilly, who impressed in the lineout, and fellow forwards Tadhg Furlong and Simon Crawford.
Cork Con had it all to do, yet they got a big boost when number 8 James Ryan grabbed a fine try at the posts after Hurley had sprung him through a gap 25 metres out.
Lyons set off on a brilliant break then, with Cathal Quinn and Robert Clune adding further movement to a cracking move, and Hurley supplied the finish by touching down in the corner. Suddenly, 'Tarf's lead was down to 17-15.
Clontarf almost replied when they were held up over the try-line, but a Lane penalty nudged them closer to a prized away triumph, even though they were forced on the defensive for much of the closing stages.
Somehow, Cork Con found a way through in deepest injury-time. Replacement Brendan Cuttriss sent Lyons dashing through a gap to score at the posts and swing this closely-fought encounter in the hosts' favour.
It was cruel luck on 'Tarf, but Constitution's infectious endeavour was rewarded and Hurley's simple conversion sealed an opening win.
Giving his reaction afterwards, former Cork Con clubman Evan Ryan, who now captains Clontarf, said: “It's very difficult to lose in the way we did. We made maybe 40 or 50 tackles in those last 10 minutes, and in the end it was a very good line that beat us.
“Myself, Richie Lane and Frank Cogan, being ex-Cork Con players, know all too well how difficult it is to beat Con when they're at home.
“That was a good game to watch today, two teams going at each other hammer and tongs, an excellent spectacle.
“I think the Ulster Bank League still has a place in Irish rugby and it's important it continues to do so. Lots of professional players who have come up through it would say the same,” he told the Irish Examiner.
Referee: Paul Haycock (IRFU)