The wing-cum-full-back had been sidelined since suffering a career-threatening double leg break in Wales’ World Cup warm-up against England at Twickenham.
But he pounced for a crucial late try to end as the Scarlets got back on track following two defeats in a row and surged back to the top of the RaboDirect PRO12 table.
Steffan Jones opened the scoring for the Dragons, in atrocious conditions at Parc y Scarlets.
With driving rain hammering down there was little opportunity for running rugby and no continuity in the opening exchanges.
Aled Thomas levelled for the hosts and they surged into the lead mid-way through the half.
A Liam Williams break saw the so far event-less encounter burst into life. The Scarlets were unable to secure a try but were awarded a simple shot at goal.
Thomas stepped up and hit the post but Gareth Maule followed up to pounce on the rebound and score.
The TMO adjudged that the ball did not sail between the posts and awarded the Scarlets the try that Thomas then converted.
He could have stretched the lead further but was off target before rediscovering his range on 33 minutes and he continued his kicking form to hand his side a 16-3 lead at the break.
The Scarlets introduced Morgan Stoddart for the second-half but he could do little to spark the game into life in difficult conditions.
But Tom Prydie kicked the scoreboard back into action following a 20-minute points drought in the second-half and the Dragons quickly continued their resurgence.
Former Scarlet Dan Evans broke down the wing for the Men of Gwent and he expertly grubbered the ball through. Scott Williams lost the ball in the slippery conditions and Hughes pounced to score.
Prydie converted but Rhys Priestland hit-back for the hosts after the Scarlets dominant scrum, built around Wales Under-20 star Samson Lee, was rewarded with a penalty – with Jonathan Edwards sent to the sin bin.
Stoddart showed no ill-effects of his long-term absence with a fine break that demonstrated his abundance of pace and power.
He was tackled short but minutes later he popped up in the corner to grab the crucial try.
