The Scarlets were left waiting on their fate after suffering a late 34-32 defeat to the Dragons in a Judgement Day thriller at the Principality Stadium.
Wayne Pivac’s side led 32-27 going into the final minutes, but a converted score from lock Matthew Screech - after a lengthy adjudication from the television match official - secured the victory for the Men of Gwent.
The Scarlets had a chance to snatch it at the death, but a drop goal attempt from replacement Rhys Patchell went agonisingly wide of the uprights.
The two bonus points the Scarlets gained from the game could still be enough to book a Champions Cup play-off spot, but there was no hiding the disappointment in the away ranks at the final whistle.
It was the Dragons who enjoyed the early pressure and led 6-0 thanks to two penalties from former Scarlets fly-half Josh Lewis.
However, the game changed on 16 minutes when Wales international Hallam Amos was yellow carded for a deliberate knock-on with a Scarlets attacker free on the outside.
Moments later, the Scarlets, playing in their change Ceredigion kit, were on the scoreboard, with Ioan Nicholas picking the gap and stretching out to cross - a score converted by Halfpenny.
It got better quickly for the ‘visitors’.
Some slick handling freed wing Johnny McNicholl and he dived over for his 10th try of the PRO14 campaign. Referee Ben Whitehouse checked with the television match official whether McNicholl had avoided the touchline, but replays clearly showed the try was good.
The Scarlets fans were celebrating a third try inside 10 minutes when scrum-half Gareth Davies sniped blindside following strong work from Samson Lee and Jonathan Davies, but it needed a great line-out steal from No. 8 Uzair Cassiem to ensure the Scarlets maintained a 17-6 advantage going into the dressing room at half-time.
Pivac would have demanded a strong start to the half, but it was the Dragons who snatched momentum straight after the break.
A score by Wales No. 8 Ross Moriarty was chalked off for a knock-on, but the Dragons were not to be denied as Screech dived over to start the comeback.
Lewis added the conversion and with David Bulbring in the sin bin, the fly-half reduced the arrears with a penalty before the home side crafted a superb score for centre Jack Dixon.
Moments later Lewis intercepted a pass from opposite number Dan Jones to send the Dragons into dreamland at 27-17, but the advantage didn’t last long.
A Ken Owens off-load set up Jonathan Davies as the Scarlets started to find some fluency again, McNicholl raced over for his second, then Halfpenny extended the advantage with a penalty.
Then came the final drama.
Wales centre Davies thought he had scored at the posts, only for the TMO to rule there had been an illegal clearout in the build-up.
That allowed the Dragons to head downfield, leading to Screech being awarded the final try following lengthy deliberation. Replacement Jason Tovey held his nerve to slot the conversion.
The Scarlets created one last chance as the clock went over the red, but Patchell’s effort was just wide.
Dragons - tries: M. Screech (2), J. Dixon, J. Lewis. Cons: Lewis (3), J. Tovey. Pens: Lewis (2).
Scarlets - tries: I. Nicholas, J. McNicholl (2), G. Davies, J. Davies. Cons: L. Halfpenny (2). Pen: Halfpenny.
Referee: Ben Whitehouse (WRU)