A nailbiting finish in Dooradoyle saw Conor Kilroy give Garryowen a what seemed a certain last gasp victory with a penalty on 81 minutes. But it was torn from their grasp by a Shannon team that refused to give up earning a David Delaney penalty in the 83rd minute to see them reach yet another playoff final.
Shannon Coach Mick Galwey spoke after the win: "It's impossible to describe that game. Conor Kilroy kicked a brilliant penalty and that kick probably deserved to win it for Garryowen.
"But I have great faith in these players and their true spirit really came through in the end - they never gave up and fair dues to them."
Garryowen boss Paul Cunningham, who confirmed afterwards that this is his last season at Dooradoyle, admitted: "That was a great kick from Conor. I thought that was the winning of it.
"The lads are just devastated. Both sides played some good rugby, given the wind out there. To be six points up (11-5) at half time, having played with the wind, to be brutally honest - I was delighted.
"Things didn't go our way at the end, but these players will be back. They won 14 out of 15 games in the League this year, and given the size of the competition, that's some record. Garryowen will be back challenging for titles but unfortunately, I won't be around to help them."
...Niall O'Brien scores one of his and 'Tarf's three tries in a comprehensive win over Cork Con at Castle Avenue...
Meanwhile in Castle Avenue, Clontarf continued their winning ways with a comprehensive win over Cork Constitution thanks to three tries from winger Niall O'Brien for a final score of 26 - 6.
Coach Phil Werahiko said: "We created the few opportunities and took them. Niall (O'Brien) and Derek (Keane) have been sharing out the tries this season, but Niall had a very good day today. He was with Connacht last season, is doing a degree this year and we're very luck to have him. He's a quality finisher."
In Division 2 Terenure dominated UCC and won by 55 points to 14 while Dolphin saw off Young Munster by 26 points to 24 to secure their place in the Division 2 final.
Clonakilty saw off Bruff by 24 - 3 in Division 3 while Suttonians beat Wanderers to ensure that all three finals will be Leinster V Munster affairs.
The Division 1 and 2 finals will take place in Lansdowne Road next Saturday while the Division 3 final has been moved to Anglesea Road on the same day. The decision to move the Division 3 final was taken to protect the Lansdowne Road pitch, which has suffered from a particularly dry winter.
IRFU Chief Executive Philip Browne said, "We realise the importance players and coaches place on the possibility of playing at Lansdowne, but unfortunately the advice given to is that the pitch would not be able to take the strain."
All supporters who attend the Division 3 Final can watch the Division 1 and 2 finals at Lansdowne free of charge.