In a free-flowing encounter, outside backs David Richards, James McCarthy (2) and replacement winger Rio Dyer crossed for Dragons tries with Kieran Williams (2), Reuben Morgan-Williams and Dewi Cross responding for the visitors.
The match was evenly poised 15-14 at the break but two quick fire penalties from fly half Arwel Robson and a dazzling finish by McCarthy put the Dragons in the ascendancy.
Williams’ powerful surge and an interception by Dewi Cross brought the Ospreys back within touching distance with time running out, but Dyer’s try in the corner on the stroke of full time sealed victory for the home side in testing conditions.
Robson pulled the strings in the first half with astute kicking to put his side on the front foot but the Ospreys showed clinical finishing with Williams in particular a constant menace with ball in hand.
Dragons dangerman Aneurin Owen was kept quiet by the Ospreys but the back three of Richards, McCarthy and Ewan Rosser wreaked havoc with their pace but the Ospreys stuck manfully to their task to stay in the game but simply ran out of time to stage a comeback.
The Scarlets underlined their dominance over their Welsh regional counterparts by completing a clean-sweep of domestic matches in the Celtic Cup as they beat Cardiff Blues A 16-12 at the Arms Park.
Since losing their opening game in the re-vamped tournament to the Ospreys Development side last season, 41-36, they have won every other regional derby, although the Blues pushed them hard. A great break by RGC back row man Tim Grey paved the way for Wales U20 lock Teddy Williams to race in for his second try of the campaign.
That gave the home side the early lead, but a try by No 8 Lewys Millin got the Scarlets back on level terms and the conversion from new signing Ryan Lamb took them into the lead. It was tense and tight throughout, but the experience of Lamb, combined with his reliable boot, kept the visitors noses in front.
He kicked two penalties before leaving and then Ioan Hughes added a third to make it 16-5 before the Blues ended their campaign on a high with a try from replacement wing Daf Smith after some clever play from outside half Dan Fish.
Fish added the extras and the Blues earned themselves a losing bonus-point at the death. The Scarlets once again finished as the top ranked Welsh region.