London Irish (6) 25
Try: Murphy, Mapusua, Armitage.
Cons: Everitt (2)
Pens: Everitt (2)
Llanelli Scarlets (10) 32
Tries: James, Easterby, M Jones, I Thomas
Pens: S Jones (2)
Cons: S Jones (3)
Llanelli Scarlets had to cling on for victory and five points after a fierce last-quarter fightback by the Exiles.
Early on they were much the better side and tries by Dafydd Jones, Simon Easterby, Iestyn Thomas and Mark Jones put them on top with 20 minutes left.
But tries by Phil Murphy and Seilala Mapusa gave home fans hope of a shock comeback, raised even higher when Scarlets' Nathan Thomas was sin-binned.
Delron Armitage added another but the gap proved just too much to claw back.
Two penalties by Barry Everitt and one for Stephen Jones were the only scores in the first 34 minutes, before Ceiron Thomas' hoof upfield set up a Scarlets attack, and Regan King supplied Dafydd James to go over in the right corner.
Jones converted and that was how it stayed until sustained Scarlets pressure was rewarded with an Easterby try.
Mark Jones slipped through the tightest of spaces to add another and Thomas' close-range barge over the line ensured a bonus point for the visitors.
Murphy scored from a forward drive to pull one back for the Exiles, before Mapusa sprinted 40 yards to score and set up a grandstand finish.
A two-man overlap set up Armitage for the final score of the night but there was no time for London Irish to get any closer than seven points.
London Irish boss Brian Smith on referee Romain Poite, who took charge when Christophe Berdos was switched to Leinster v Gloucester.
"His performance left a lot to be desired. We were ranked the third team in England last year so why were we bumped for Gloucester?
"ERC is run out of Dublin so are favours being done for Leinster?"
Scarlets head coach Phil Davies:
"We were delighted to get the win and bonus point. It was a big game for us because I wasn't pleased with our last outing against Newcastle.
"There's a lot of pride in the squad and we wanted to perform well. It was a very professional performance."
London Irish: Horak; Ojo, Mapusua, Catt (capt), Tagicakibau; Everitt, Hogdson; Hatley, Paice, Skuse, Roche, Hodgson, McCullen, Danaher, Leguizamon.
Replacements: D Murphy for Danaher (47), Coetzee for Paice (47), Tiesi for Catt (49), Rees for Hodgson (49), Magne for Leguizamon (51), Armitage for Ojo (65), Lea'aetoa for Skuse (71).
Scarlets: C Thomas; D James, King, G Evans, M Jones; S Jones, Peel; I Thomas, M Rees, Dunlea, Cooper, Afeaki, S Easterby (capt), G Thomas, Popham.
Replacements: Manu for Dunlea (59), A Jones for Afeaki (57), N Thomas for Easterby (67).
Not Used: Gravelle, Stuart-Smith, Daniel, B Davies.
Referee: C Berdos (Fra).