London Irish backs coach Richard Whiffin insists his side only had themselves to blame as they let a half-time lead slip to Scarlets in the LV= Cup.
Former Scarlet Andy Fenby had put the visitors ahead at the interval, with Myles Dorrian cancelling out Steve Shingler's two early penalties after both Ken Owens and Shingler were sent to the sin-bin.
But Harry Robinson, Adam Warren, and Kyle Evans all went over for the hosts in the second-half, and not even a late Theo Brophy-Clews score could rescue London Irish from their third defeat of the competition.
"We were the masters of our own downfall, to be honest," said Whiffin.
"We did well in the first half and they were down to 13 men, but we went away from our game-plan in the second half and we just weren't able to control the middle third of the field.
"It didn't help that we made individual errors and some of those were from our more experienced players.
"We took our foot off the gas and allowed the Scarlets back into the game."
Meanwhile Scarlets skipper Ken Owens – returning for his first game since September after a neck injury – admitted the prize of a playing spot for the rest of the season spurred his side on to come back.
It was the Llanelli outfit’s first win of the campaign, although neither side can qualify for the knock-out stages.
Owen said: "It was a tough game. We started pretty well but we couldn't get a foothold. There was a bit of error that crept into our game and we went down to 13 men.
“But we did well in the second half and got our rewards. The boys put a big shift in and we said before the game that there are places up for grabs for the rest of the season.
"I've got plenty to work on over the next few weeks but it was good to get that initial hit-out.
"I haven't been selected in the Wales Six Nations squad and there are three very good hookers who have been. It's up to me try to regain my spot at some stage during the season."
Scarlets: Lewis (Evans 3), Robinson, Climo, Warren, Phillips, Shingler, Williams, John (W Jones 40), Owen, Edwards (Adriaanse 56), Earle (Bennett 11), Rawlins (Bennett 43), Day, Boyde (Harris 40), Pitman (Payne 56)
Replacements not used: Hardy, D Jones
London Irish: Homer (Lyons 70), Short (Sheridan 52), Fowlie, Griffin (Sheridan 60), Fenby, Dorrian, Allinson (O'Leary 56), Harris (Palframan 70), Stevens (Mayhew 60), Halavatau ('Aulika 60), Rouse, Cox (Brophy Clews 70), Low (Curry 40), Gilsenan, Leo
Tries: Robinson, Warren, Evans
Conversions: Shingler 3
Penalties: Shingler 2
Tries: Fenby, Brophy-Clews
Penalties: Dorrian 2
Referee: Craig Maxwell-Keys
Tickets for this year's LV= Cup Final on 22 March at Franklin's Gardens are now on sale. Click here to snap one up from just £20 for adults, £10 for juniors to see who will win the first silverware of the season.