It was honours even in the first ever AIB League match to take place at the redeveloped Thomond Park as Tadhg Bennett kicked a late, levelling penalty for Shannon against their arch rivals Garryowen.
Number 10 Bennett ensured the 17-17 stalemate in injury-time, after winger Lorcan Bourke's 78th-minute try had nudged Garryowen into a winning position.
Bennett and Garryowen full-back Conor Kilroy swapped place-kicks for a 6-6 interval score-line. Both sides opened up as the intensity increased in the second half.
Man-of-the-match Fiach O'Loughlin touched down for a 14-12 Shannon lead but Kilroy put Bourke over to set up a tense finish in which Bennett brilliantly held his nerve.
Meeting for the 22nd time in the AIB League and for the first time under floodlights, Shannon and Garryowen served up an after dark thriller.
In truth, neither side deserved to lose but with the two Limerick giants struggling for early season form, down in 11th and 12th in the Division One table, tonight's draw means they have lost further ground on the league pace-setters.
The opening quarter was cagey and neither the hosts or Garryowen, who were hoping to end a three-match losing streak in the league, could find their rhythm.
Scoring chances were few and far between, but Kilroy and Munster's Kieran Lewis and Ciaran O'Boyle looked dangerous when on the ball for Garryowen.
Shannon had their scrum half and captain Fiach O'Loughlin back in the team after his recovery from a knee injury, as well as Munster and Ireland prop Tony Buckley bolstering their pack.
Bennett and Kilroy kicked a brace of penalties each, the former having put Shannon 6-3 up before Kilroy smacked over a fine effort in the 35th minute.
Shannon lost their inside centre John Clogan to a yellow card before half-time but they made the best possible start to the second half.
The livewire O'Loughlin, who passed a late fitness test to start, scored a splendid try five minutes after the restart.
Bennett missed the conversion But Shannon's tails were up as they looked to gain revenge from last May's 31-6 semi-final defeat by the same opposition.
The influential Kilroy snapped Garryowen back into a 12-11 advantage with two meaty kicks.
Shannon sneaked ahead again when Bennett split the posts for the third time.
As the game entered the final ten minutes, Geoff Moylan's men, with their pack on song, looked set to grind out the win by keeping it tight.
However, Garryowen managed to create a try out of nothing with some superb counter-attacking which ended with Bourke getting over in the right corner.
The light blues rumbled forward off a midfield lineout, going through two phases before the ball was moved at pace and Kilroy was the link man, taking Andrew Finn out of the game with the pass which put Bourke away.
Crucially, Kilroy could not convert from wide out and Garryowen's efforts were thwarted, four minutes later, when Bennett kept his cool with a shot from in front of the posts.
Prop Buckley, left out of the Munster squad for the game against Sale Sharks on Sunday, shone in a Shannon pack which dominated.
Yet Garryowen did have the best backs on view in Ciaran O'Boyle and the outstanding Kilroy.
Indeed, two great breaks by O'Boyle almost yielded tries but each time the Shannon defence held firm.
Shannon: A Finn; R Mullane, A Thompson, J Clogan, S Kelly; T Bennett, F O'Loughlin (capt); G McNamara, M Essex, T Buckley, P O'Brien, F Walsh, J O'Connor, E Grace, D Quinlan.
Garryowen: C Kilroy; L Bourke, K Lewis, C Doyle, Ciaran O’Boyle; A Kingsley, Cillian O'Boyle; R Brosnan, M Sherry, D Lavery, M Melbourne, F McKenna, P Neville (capt), C Hartigan, D Sherry.
Referee: David Keane (IRFU)
Scorers: Shannon: Try: Fiach O'Loughlin; Pens: Tadhg Bennett 4
Garryowen: Try: Lorcan Bourke; Pens: Conor Kilroy 4
HT: Shannon 6 Garryowen 6
