The Dragons took the victory deservedly by 28-21, outscoring Ulster by three tries to two.
After a scrappy first half, Ulster led 6-3, courtesy of two penalties from David Humphreys to one from Ceri Sweeney. A further Humphreys effort shaved the post. Ulster had a fair amount of possession in the first half, but their attacking gambits were chiefly kicks to the corner from Humphreys.
With the Ulster backrow already shorn of Neil McMillan and Andy Ward, the last thing they needed was the injury to Roger Wilson that necessitated his replacement by Matt Mustchin.
The second half wasn't very old before the dangerous Kevin Morgan sprinted in unmolested from the Ulster 22 to put The Dragons ahead. Sweeney's conversion moved the score to 10-6 to the Dragons.
Humphreys and Sweeney exchanged penalties to move the scoreboard to 13-9 before Ulster's best moments of the match. A sizzling 80 metre run from Tyrone Howe was the precursor to an intelligent Humphreys kick that enabled Neil Best to score a try in the corner.
Ulster's joy lasted but five minutes, though, as Adam Black crossed for The Dragons as they opened up the Ulster defence again to restore the four point lead at 18-14 to the Dragons.
When Nathan Brew glided over in the 72nd minute, the Dragons were pretty much home and dry, with Sweeney's conversion nudging the score to 25-14.
Ulster did produce a late score from Ronan McCormack in injury time, converted by Humphreys, to close the gap to 25-21, but any late Dragons discomfort was eased by Sweeney's late penalty to leave the final score 28-21 to The Dragons.
The result leaves The Dragons in second position in the League on 18 points. Ulster pick up a bonus point to leave them on 9 points.
Ulster: B Cunningham; T Bowe, P Steinmetz, K Maggs, T Howe; D Humphreys (capt), K Campbell; S Best, P Shields, R Moore, G Longwell, M McCullough, C Feather, N Best, R Wilson.
Replacements: N Brady, R McCormack, R Frost, M Mustchin, N Doak, P Wallace, J Bell.
Dragons: K Morgan; G Wyatt, P Montgomery, S Tuipulotu, N Brew; C Sweeney, G Cooper; R Snow, S Jones, R Thomas, I Gough, M Owen, J Ringer, J Forster, R Bryan.
Replacements: J Richards, A Black, G Robinson, P Sidoli, R Beattie, S Winn, G Baber.
Referee: Malcolm Changleng (Scotland)