A late try by man-of-the-match Ray Niland on the wing won vital points for Garryowen in this mid-table clash.
Lansdowne looked secure just before half-time after their openside flanker Chris Pratt broke through a poor Garryowen defence after good work by winger Fiachra Baynes and outhalf Alan McGowan, who also converted.
But with just a penalty each from McGowan and Garryowen scrumhalf Billy Treacy, it was all to play for at half-time, and Garryowen went hell for leather for the remainder of the game.
Lansdowne barely left their own half from there on as they were pinned back while the Limerick side piled on the pressure. However, their stout defence held out against the onslaughts.
Garryowen might have scored three tries midway through the half, but they let themselves and their supporters down by conceding easy relieving penalties to McGowan's boot.
The deserved moment came right on the stroke of full time when the Garryowen pack broke through the tiring Lansdowne defence. A quick break by Treacy put Niland in complete command. He broke the midfield tackles for a try wide out and Treacy added the extra points.
Scoring Sequence: 13 mins: B Treacy pen 0-3; 23 mins: K McGowan pen 3-3; 30 mins: C Pratt try A McGowan con 10-3; 59 mins: B Treacy pen 10-6; 81 mins: R Niland try B Treacy con 10-13.
LANSDOWNE: B Doherty, R Dolan, D O'Mahony, A Magro, F Baynes, A McGowan, S Whelan, E Bohan, R Fallon, A McKeen, G Fulcher, G Quinn, S Rooney (Capt), C Pratt, S O'Connor. Replacements: O Ennis for Fallon, B Cusack for O'Connor, K Becker for Whelan, B Geraghty for Doherty.
GARRYOWEN: D O'Riordan, C Tupeniere, R Niland, C Foley, K O'Riordan, B Treacy, A McGuckian, J Staunton, P Humphries, J Giltenane, E Kelly, J Langford, C Varley (Capt), C Hartigan, J O'Sullivan. Replacements: S Leahy for Kelly, P Malone for Varley, S McCarthy for McGuckian, C Richardson for Foley.