James extended his Heineken Cup try-scoring record
Scarlets: (17) 20
Tries: Peel, James
Cons: S Jones (2)
Pens: S Jones (2)
London Irish: (6) 16
Pens: Everitt (2), Geraghty
Llanelli Scarlets will host Munster in the Heineken Cup quarter-finals after surviving a London Irish fightback to complete a 100% record in their pool.
With the home side already guaranteed a home quarter-final and the Exiles out, early tries from Dwayne Peel and Dafydd James pointed to a routine win.
Replacement Shane Geraghty threw James the interception pass for his try, but a Geraghty try inspired the comeback.
Ten points from Stephen Jones' boot saw the Scarlets home, despite late scares.
Playing against a stiff breeze at Stradey Park, the Scarlets opened with a penalty from outside-half Jones.
That was cancelled out when opposite number Barry Everitt converted a kick set up by his own excellent midfield break.
A huge Scarlets scrum drive from a London Irish put in on the Exiles' 22 led to the first try.
Alix Popham picked up and off-loaded well to Peel, whose sharp run took him outside Everitt's despairing cover and in under the posts.
The visitors rallied, but a long midfield pass from Geraghty was plucked out of the air by James who ran in from 65m, extending his Heineken Cup record number of tries to 27.
Everitt pulled back a penalty to make it 17-6 at the break, and the Exiles made a bright start to the second half.
That was rewarded when Geraghty breached the Llanelli side's stretched midfield defence to cross from short range.
Stoddart denied Topsy Ojo at the death
Geraghty converted, and added a 66th-minute penalty to close the gap to a point.
The Scarlets spurned an easy kick at goal, but Jones later eased Stradey Park nerves with an excellent 52m penalty.
Topsy Ojo nearly snatched victory from the Scarlets' grasp, but his thrilling touchline run, kick and chase was just thwarted by Morgan Stoddart and Darren Daniel.
Exiles lock Nick Kennedy showed his frustration with a late sin-binning for punching Simon Easterby as the west Wales side joined the select band of clubs to have won all six of their Heineken Cup pool games.
Scarlets director of rugby Phil Davies:
"I am very proud of what we have achieved in this competition so far.
"I was pleased with the win and the fact that we have got a home quarter-final.
"We were a bit sloppy at times, but you have to give London Irish credit for the way they played, they kept the ball extremely well.
"From my time in the Premiership I knew how good a side they are. To be fair, we had a go in the first half, gave ourselves a platform, but could never get away from them."
London Irish coach Brian Smith:
"We were disappointed in the first half, we took a calculated risk to go with the wind because we freshened up the side and knew we would be a little bit rusty.
"We wanted to get a good start, but it didn't really work out that way. In the second half I was proud of the players, it was very gutsy and very courageous. We can definitely take something out of the game.
"We pushed a Scarlets side who, ball in hand, are as good as any side who have played this season and are worthy winners of our pool.
"I have been pleased with our performances in Europe this season, obviously not the results, but hopefully we have given our fans something to smile about because we certainly have had a crack."
Scarlets: Stoddart, James, King, G. Evans, Watkins, S. Jones, Peel, I. Thomas, Rees, Dunlea, A. Jones, MacLeod, Easterby, G. Thomas, Popham.
Replacements: Daniel for G. Evans (80), Manu for Dunlea (59), D. Jones for G. Thomas (59). Not Used: Owen, Cooper, Stuart-Smith, C. Thomas.
London Irish: Horak, Ojo, Mapusua, Flutey, Bishop, Everitt, Rees, Lea'aetoa, Paice, Skuse, J. Hudson, Roche, McCullen, Magne, P. Murphy.
Replacements: Geraghty for Horak (29), S. Armitage for Everitt (46), Willis for Rees (61), Collins for Lea'aetoa (68), Russell for Paice (48), Fitter for Skuse (61), Kennedy for Roche (55).
Sin Bin: Kennedy (80).
Referee: Christophe Berdos (France)