Judgement Day: Late try edges Dragons to win 34-32 against Scarlets
Matthew Screech scored the winning try two minutes before the final whistle as Scarlets' hopes of a European Champions Cup spot suffered a blow following a 34-32 defeat to Dragons at the Principality Stadium.
The Dragons trailed 17-6 at half-time but 21 unanswered points in the third quarter set up their best win of the season.
Screech scored two tries for them, Jack Dixon the other with Josh Lewis kicking two penalties and three conversions and Jason Tovey one.
Johnny McNicholl scored two tries for Scarlets, Ioan Nicholas, Gareth Davies and Jonathan Davies the others, with Leigh Halfpenny adding two conversions and a penalty.
Dragons took a third-minute lead when Lewis picked himself up after being tackled late by Dan Jones to send over a penalty.
The first 15 minutes were easily forgettable as neither side could make any impact against resolute defences and it was left to Lewis to extend Dragons' lead with his second penalty.
Soon afterwards, the Gwent region, suffered a blow when Hallam Amos, who was making his final appearance for them before his transfer to Cardiff Blues, was yellow carded for a deliberate knock-on.
Scarlets took immediate advantage as Nicholas rewarded a period of pressure by forcing his way over for Halfpenny to convert for his side to lead 7-6 at the end of the first quarter.
In the absence of Amos, Scarlets turned down two kickable penalties and their decision was rewarded when McNicholl outflanked the cover defence to squeeze in at the corner.
Amos returned but he could not stem the tide as Gareth Davies sneaked over from close range and despite Halfpenny missing both conversions, Scarlets were in firm control at half-time with a 17-6 advantage.
Within two minutes of the restart, Dragons looked to have reduced the deficit when Ross Moriarty kicked ahead and crashed over but the TMO ruled that the Welsh international number eight had lost possession of the ball when it rebounded back off a post.
Despite this setback, Dragons maintained their momentum to pick up a try from Screech with David Bulbring yellow carded in the aftermath before Scarlets' prop, Samson Lee, was fortunate to escape another for a tip tackle.
Lewis missed a penalty before Dragons produced a superb try when Amos and Aaron Wainwright combined cleverly for Dixon to score.
Scarlets were stunned when Lewis hit them with a third try after intercepting a pass from Dan Jones to give Dragons a 10- point lead going into the final quarter.
Jones paid the penalty for his error as he was replaced by Rhys Patchell before Bulbring returned in time to see Jonathan Davies secure a bonus point with his side's fourth try.
McNicholl brought his side level with his second before Halfpenny's conversion and penalty looked to have seen Scarlets home until Screech's effort crushed them with his try being awarded after countless replays that appeared to suggest that the lock had been dragged down short of the line.