Blues (6) 9 Pens: Blair 3. Scarlets (11) 30 Tries: L Williams 2, Day, Daniel. Cons: S Jones 2. Pens: Priestland 2.
Scarlets wing Lee Williams squeezes over at the corner flag
The Scarlets ensured that they will definitely be playing in the Heineken Cup next season with a hard-fought win against the Blues at Cardiff Arms Park.
Wing Lee Williams went over in each half and set up Dominic Day for his try with a fine midfield break, while Darren Daniel scored in injury time.
The Blues had to make do with three penalties from full-back Ben Blair.
The result means Newport Gwent Dragons must now play-off against an Italian side for a Heineken Cup place.
The Scarlets began looking like a team that had lost its previous four Magners League matches, while it was the hosts who looked comfortable.
Early dominance from the Blues pack applied just enough pressure to keep the Scarlets on the back foot and earn two penalties that Blair eased between the posts.
Rhys Priestland replied with his first opportunity for the Scarlets, who had started to make some inroads into the Blues' half, thanks in no small part to captain David Lyons.
The former Australia number eight led from the front, driving into contact and giving his fellow forwards a target - and an example - to follow.
One such drive created space on the left and the ball was spun swiftly along the line to wing Williams, who squeezed in at the corner flag despite Richie Rees' tackle.
The try was not clear-cut, however, as Williams seemed to have lost control of the ball in the challenge, although television match official Tony Rowlands awarded the score.
Prestland missed the conversion, while Blair was wide with a penalty attempt for the Blues on the half-hour.
But then the home side lost back-row Robin Sowden-Taylor to the sin-bin for slowing down ball, Priestland kicking the resulting penalty for a 11-6 lead at half-time.
The Scarlets stretched their lead after the break when Williams found a huge hole in the Blues midfield to scamper through and send lock Day over for an unconverted try.
Sensing a victory that would ensure Heineken Cup qualification for next season, Scarlets director of rugby Nigel Davies called for his senior players held in reserve on the bench.
Iestyn Thomas, Simon Easterby and Lions selection Matthew Rees arrived on the pitch.
Blair pulled back three points for the Blues with his third kick of the night after tempers had boiled over between the two sides.
More Scarlets experience was needed and half-back pairing Stephen Jones - another Lion - and Martin Roberts replaced Priestland and Gavin Cattle.
But it was one of the Scarlets' rookies - Jon Davies - who helped seal the result as the centre came flying up in defence to floor Ceri Sweeney, knocking the ball loose for Williams to gather and race under the posts.
Jones' conversion put Scarlets 23-9 ahead with 17 minutes left, a lead that would surely ensure they finished above the Dragons in the final Magners table.
Wing Daniel gave the score an even greater gloss - and a bonus point to go with it - with a breakaway try in the last move of the game, picking up a loose ball in his own 22 and scorching upfield.
Even if Dragons beat Leinster on Saturday with a bonus point and Scarlets lose to Ulster, the men from Newport cannot overhaul the Scarlets' points total.
So it will be the Dragons who face a play-off against the third-placed Italian side for the 24th and last Heineken Cup place on offer, with that game taking place on 29 May.
The double blow for the Dragons is that the four of their players who have been selected for Wales' summer tour to North America will now have to withdraw from the national squad.
The first Test against Canada is the day after the Dragons' play-off, while Wales then play the USA a week later.
Blues director of rugby Dai Young: "There was a clear difference in the two teams: one had a lot to play for and one had little to play for and was running on empty.
"It's disappointing because you never want to lose at home and you never want to lose to one of your closest rivals.
"We said in the dressing room before the game that we... wanted to have a bit of pride in our performances and finish off strongly. That wasn't the case tonight."
Scarlets director of rugby Nigel Davies: "The pressure was building on us, there's no doubt about that and a lot of it was down to ourselves.
"It's unfortunate this year that we're congratulating ourselves for just about qualifying for Europe.
"But we showed today - and particularly the youngsters in the squad showed today - the potential within the team and they've got to believe now and press forward."
Blues: Ben Blair; Richard Mustoe, Jamie Robinson, Gareth Thomas, Chris Czekaj; Ceri Sweeney, Richie Rees; John Yapp, T Rhys Thomas, Faao Filise, Bradley Davies, Deiniol Jones, Ben White, Robin Sowden-Taylor (capt), Maama Molitika. Replacements: Gary Powell for Filise (60), Ross Johnston for T. Thomas (64), James Down for Davies (62), Scott Morgan for White (70), Darren Allinson or Rees (60), Dai Flanagan for Sweeney (74), Nicky Robinson for J. Robinson (46).
Scarlets: Daniel Evans; Darren Daniel, Rob Higgitt, Jon Davies, Lee Williams; Rhys Priestland, Gavin Cattle; Phil John, Ken Owens, Deacon Manu, Lou Reed, Dominic Day, Dafydd Jones, Rob McCusker, David Lyons (capt). Replacements: Iestyn Thomas for John (49), Matthew Rees for Owen (49), Aaron Shingler for Reed (77), Simon Easterby for McCusker (49), Martin Roberts for Cattle (63), Stephen Jones for Priestland (62), Ceiron Thomas.
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