Dafydd Jones, Simon Easterby, Iestyn Thomas and Mark Jones crossed to leave the Exiles looking dead and buried heading into the final quarter.
But Irish ran in three quickfire tries through Phil Murphy, Seilala Mapusa and Delon Armitage as Llanelli took their foot off the pedal to blow the match wide open.
With the visitors’ initial flurry seen off, Irish made settled and were rewarded with a Barry Everitt penalty.
Stephen Jones levelled with a penalty as the momentum continued to shift with Irish’s cause taking a blow with Declan Danaher being sin-binned.
Everitt landed his second penalty but the Exiles’ line was breached in the 34th minute with a loose kick from Paul Hodgson starting Llanelli’s move.
Ceiron Thomas returned the chip ahead with interest, the ball was recycled and fed to Regan King who showed quick hands to send Dafydd James in at the right corner.
Stephen Jones converted to give Llanelli a 10-6 half-time lead they stretched just seven minutes after the interval.
Irish’s line came under sustained pressure and eventually Easterby succeeded and Jones added the extras.
Winger Mark Jones piled on the misery for the Exiles, by taking King’s pass and rounding Ojo to the line.
Prop Iestyn Thomas barged over from close range in the 60th minute but Irish stemmed the tide with a try of their own with Phil Murphy driven over from a line-out.
The Exiles scented a remarkable comeback was on the cards as Mapusa dashed 40 yards to cross.
Armitage touched down as Irish capitalised on a two-man overlap but they could not add to the score.
Tries: D. Murphy, Mapusua, D. Armitage. Cons: Everitt 2. Pens: Everitt 2.
Horak, Ojo, Mapusua, Catt, Tagicakibau, Hodgson, Everitt, Hatley, Paice, Skuse, Roche, J. Hudson, McCullen, Danaher, Leguizamon.
Pedro Tiesi for Catt (49), Rees for Hodgson (49), Coetzee for Paice (47), Lea’aetoa for Skuse (71), Magne for Danaher (47).
Tries: James, Easterby, M. Jones, I. Thomas. Cons: S. Jones 3. Pens: S. Jones 2.
C. Thomas, James, King, G. Evans, M. Jones, S. Jones, Peel, I. Thomas, Rees, Dunlea, Cooper, Afeaki, Easterby, G. Thomas, Popham. Replacements: A. Jones for Afeaki (57), N. Thomas for G. Thomas (10).
Romain Poite (France).