Sio Tomkinson grabbed a try double on his final club appearance as Dragons ended the season with derby day disappointment at Judgement Day in the capital.
The Men of Gwent went into the final BKT United Rugby Championship game of the campaign looking to secure a first season double over the West Walians since 2007/08.
But it was largely a frustrating afternoon for Dai Flanagan’s side who ended the league campaign in 15th place in the standings.
Dragons had played five previous matches at Cardiff City Stadium in all tournaments but had lost them all.
And they were always up against it after first half tries from Kemsley Mathias and Dan Davis put the Scarlets into a 17-3 lead.
Two quickfire scores from wing Tomi Lewis wrapped up the bonus point before Tomkinson, on his final appearance for the club, grabbed a double.
Dai Flanagan made four changes with Ryan Woodman in the back row while there was also a start up front for hooker Brodie Coghlan.
Centre Joe Westwood was recalled in midfield alongside Aneurin Owen, who made his 50th appearance.
The final change was a return for Rhodri Williams at scrum half, with the number nine also named captain.
The recalled Westwood and Woodman both carried hard in the opening minutes but a penalty for collapsing the scrum gave Sam Costelow the chance to kick into the 22 and set up an early home attack.
Dragons were defending with line speed and a scrum penalty, this time as Scarlets collapsed, allowed Reed to kick into enemy territory for the first time.
Chris Hollis carried strongly, after Owen released Westwood to open space, before a no arms tackle form Sam Lousi on Rhodri Jones gave Reed a first shot at goal that he nudged over.
Scarlets threatened down the left, but Ryan Conbeer kicked the ball out on the full.
They did, however, draw level when Dragons were pinged at the breakdown and Costelow slotted his first kick of the afternoon.
The Scarlets playmaker missed another attempt five minutes later, after Dragons were penalised for side entry at a fiercely contested breakdown.
Rio Dyer burst into life when he took a cross kick and rolled out of tackles, with Williams turning Ioan Nicholas with a kick to the corner.
Scarlets, though, were awarded a penalty at scrum time to give them a first period of pressure in the 22, and they duly made it count as the maul rumbled over with Mathias getting the opening try.
The restart saw Owen tackled high by Eddie James and the resulting TMO gave the Scarlets midfielder a yellow card.
Another penalty saw Dragons go to the corner and then win a five-metre scrum, but a cross field kick saw Dyer immediately put into the tramlines by Nicholas.
Scarlets compounded the wasted opportunity as the 14-men freed up Tomi Lewis, after a slick Lousi offload, and he sent Davis over for the score, despite appeals for a forward pass in the build-up.
Subdued Dragons, who saw a limping Wainwright replaced by Dan Lydiate at the break, needed a quickfire response after the break.
Instead a loose pass from Dyer, after he scrambled across the field, was picked off by wideman Lewis who raced over unopposed to score.
Dragons needed to act quickly with Rosser and Williams combining to keep the ball alive before Hollis arched a run down the left.
Flanagan changed up his front row but it did little to stop Scarlets added a fourth through Lewis, after Ryan Elias managed to avoid a knock on in midfield after a low pass.
Tomkinson was introduced just before the hour and his first touch saw him dot down out wide for a first try for Dragons.
A Hughes grubber was collected by Westwood and he was dragged down by Conbeer as Dragons went to the forwards to apply pressure in the close quarters.
Che Hope looked to inject fresh pace late on, with his tap and go sending Westwood up close, before pressure at scrum time freed up Reed to send Tomkinson over again.
Costelow eased any home nerves with a penalty with six minutes remaining to ensure Scarlets took maximum points.
Timeline:
09m Reed p 0-3
15m Costelow p 3-3
29m Mathias t Costelow c 10-3
38m Davis t Lloyd c 17-3
44m Lewis t Costelow c 24-3
54m Lewis t 29-3
58m Tomkinson t 29-8
69m Tomkinson t Reed c 29-15
74m Costelow p 32-15
Dragons RFC: Ewan Rosser, Rio Dyer, Joe Westwood, Aneurin Owen (Hughes 31), Chris Hollis (Tomkinson 57), Will Reed, Rhodri Williams (Hope 66); Rhodri Jones (Martinez 53), Brodie Coghlan (Benjamin 53), Chris Coleman (Arhip 53), Ben Carter, Matthew Screech (Nott 61), Ryan Woodman, Taine Basham, Aaron Wainwright (Lydiate 40)
Replacements: James Benjamin, Rodrigo Martinez, Dmitri Arhip, George Nott, Dan Lydiate, Che Hope, Steff Hughes, Sio Tomkinson
Scarlets: Ioan Nicholas; Tomi Lewis, Johnny Williams, Eddie James, Ryan Conbeer, Sam Costelow, Gareth Davies; Kemsley Mathias, Ryan Elias, Harri O’Connor, Alex Craig, Sam Lousi, Taine Plumtree, Dan Davis, Carwyn Tuipulotu
Replacements: Shaun Evans, Wyn Jones, Sam Wainwright, Morgan Jones, Jarrod Taylor, Kieran Hardy, Ioan Lloyd, Macs Page
Referee: Craig Evans (WRU)
