A last-minute try by number eight Ben Gissing, coolly converted by substitute Jim Dempsey, earned Clontarf a deserved share of the points at Dooradoyle on Saturday.
The Dublin side found themselves 14 points behind with only 10 minutes to go, but they hung in bravely and eventually got the draw their efforts merited.
The first half was a poor affair and ended level on six points each, but Garryowen gained the upper hand on the turnover, with John Langford hugely influential in the lineout and Billy Treacy looking a potential match-winner as he knocked over three dropped goals and four penalties.
But he failed to convert Killian Keane's try and Clontarf saw their chance.
Mark Woods and Dave O'Brien landed their early penalties, and after Dempsey came on for Woods, he kept the scoreboard ticking over. Andy Cullen scored their first try, and finally they drew level when Gissing forced his way over and Dempsey's conversion was the last kick of a hard-fought and enjoyable second half.
GARRYOWEN: K Keane; C Tupiniere, R Niland, C Foley, C Richardson; W Treacy, S McCarthy; J Staunton, P Humphreys, J Giltinane, E Kelly, J Langford, C Varley, P Malone, J O'Sullivan. Replacements: S Leahy for Kelly, C Hartigan for Malone.
CLONTARF: K Nowlan; A Reddan, D O'Brien, J Downey, O Winchester; M Woods, M Walls; W O'Kelly, M Kennedy, A Clarke, D Sheehan, A Wood, D Quinn, A Cullen, B Gissing. Replacements: J Dempsey for Woods, R O'Reilly for Walls, T Foucher for O'Kelly.
Referee: P Eakin (Leinster).