Northampton Saints ran in four tries to seal a spot in the EDF Energy Cup semi-finals.

Saints had to play the last 10 minutes with 14 men, but two tries from Chris Ashton, and one from Bruce Reihana and Sean Lamont sealed the win and the bonus point against a speedy and skilful Scarlets.

Saints needed the fourth try as Saracens came back to win at Bristol to book their place at the Ricoh Arena in Coventry.

But Saints were made to work hard. Cieron Thomas missed a first minute penalty from the touchline and he missed a conversion from the same spot five minutes later as Scarlets waltzed through Saints' defence.

Thomas dummied past Stephen Myler to get within five metres of the line and centre Regan King eased through the green, black and gold line to open the scoring.

Saints were barely awake and it was 10-0 after eight minutes as quick hands released Morgan Stoddart on the left wing and he stormed past two defenders to touch down.

Saints got straight back into the game after a thrusting run from Ben Foden won them a penalty. They kicked into the corner and from the lineout Chris Ashton dived over. Myler missed the touchline conversion to leave Scarlets ahead at 10-5 after 13 minutes.

Scarlets were looking threatening with every attack and earned a penalty right in front that Thomas knocked over to make it 13-5.

After Ashton failed to turn open space into a try, Saints won a penalty 23m out and Myler landed it to make it 13-8.

On 24 minutes Myler had the chance to reduce the arrears to two, but just missed from 30m from the left.

Five minutes later Saints finally got some quick ball to go wide. Bruce Reihana's pass looked forward but Ashton dived into the corner and the TMO gave the try to put Northampton level on 13-13 as Myler missed the touchline conversion.

A quick lineout throw almost saw Scarlets score on the stroke of half-time as Rob Higgitt charged for the line, but the TMO ruled it didn't get over the line.

Saints come out fired up and after five minutes Foden released Reihana down the blindside to power over from 20m. Myler landed the touchline conversion to put Saints ahead at 20-13 for the first time.

But Myler missed a 30m penalty that he should have got, and Stephen Jones came on to release the pressure with a thunderous kick that Reihana dropped into touch.

Now in Saints land No. 8 David Lyons looked to have scored for the visitors, but the TMO found that Myler had ripped the ball out of his hands just before he fell onto the line.

Jones missed a penalty from 47m, but Myler made no mistake from 48m to put Saints 23-13 ahead.

And on 65 minutes Sean Lamont cut a beautiful line to crash over from 7m for the all important fourth try to make it 30-13 as news filtered through that Saracens were now winning at Bristol.

But on 70 minutes Saints were hit with the hammer blow of James Downey being sin-binned after he took out Regan King off the ball.

And two minutes later Scarlets made the man advantage count as replacement Jonathan Davies dived over in the corner. Jones converted to make it 30-20 with seven minutes to go.

But a brilliant driving maul from the forwards got Saints deep into Scarlets territory and they won a penalty, which Myler landed from 30m to make it 33-20 and Saints played out time to win and win pool D.

Northampton Saints: Reihana; Ashton, Mayor, Downey, Lamont; Myler, Foden; Smith, Shields, Murray, Fernandez Lobbe, Lawes, Hopley, S Gray, Wilson.
Replacements: J Gray, Tonga'uiha, Day, Easter, Dickson, Spencer, Diggin.

Scarlets: Stoddart; Higgitt, King, G Evans, M Jacob; C Thomas, Martens; I Thomas, Owen, Meeuws, D Jones, Day, N Thomas, Easterby, Lyons.
Replacements: John, Rees, Turnbull, G Thomas, Roberts, S Jones, Davies.

Att: 12,042