Ulster moved to within four points of RaboDirect PRO12 leaders Leinster after they defeated the Scarlets 26-13.
Tries from Tommy Bowe and Tom Court, along with a double from Paddy Jackson helped a resilient Ulster start the St Patrick's celebrations early.
The Welsh region hit back with a well-taken try from Gareth Davies to supplement the boot of Olly Barkley, but lacked the discipline and creativity to break down the home defence.
The visitors were competitive throughout, but looked bereft of ideas at times, and there is little doubt that Ulster were worthy winners to kick off what could be a seminal weekend for Irish rugby.
It was the hosts that made the superior start, and were nearly rewarded for their efforts on two minutes when Jared Payne sliced through a passive Scarlets' defence before putting Bowe away in the corner. Unfortunately for his side, the Irish winger fumbled with the line at his mercy.
The Welsh visitors weathered Ulster's early onslaught well, establishing some field position of their own through former England star Barkley, but failed to make any real inroads in the home 22.
It was Ulster, therefore, who regained ascendancy, and efficiently established a platform in the Scarlets half of the field. Thus it was the hosts that opened the scoring on 15 minutes when the Welsh full-back Jordan Williams lost control just yards from the try line.
A grateful Jackson swept up the stray ball and touched down unopposed. The fly-half's effort was converted by Pienaar to give the Belfast side a 7-0 lead.
Ulster doubled their advantage just two minutes later when Jackson fed Bowe to score under the posts. Naturally enough, Pienaar made no mistake with the simple conversion.
The Irish province was certainly dominating the opening quarter of the game, therefore. But their momentum was hindered somewhat on 23 minutes when loosehead Callum Black was carried off injured, to be replaced by Irish international, Court.
Barkley got his side on the scoreboard on 32 minutes when he coolly slotted a neat penalty to make it 14-3 to the Irishmen.
But the Scarlets' respite was short-lived. Another well-worked inter-change between Bowe and Jackson on 34 minutes saw the fly-half get over for his second try of the evening. Pienaaar duly added the extra points to make it 21-3 to his side.
Scrum=half Davies responded for the Welshmen on 36 minutes to narrow the deficit. Barkley again did the needful to reduce Ulster's lead to eleven. The Scarlets centre had another chance on the stroke of half time when the visitors were awarded a penalty, but failed to capitalise on the opportunity.
The visitors noticeably upped the tempo after the interval, but struggled to retain possession. The opening part of the half was rather fractured, with both teams struggling to achieve any real fluidity.
Ulster's attempts to close the game out were not helped by Pienaar missing two penalties, albeit difficult ones. Barkley reduced Ulster's lead further on 61 minutes to make it 21-13 to the hosts.
Irish blindside Stephen Ferris received a rapturous ovation a couple of minutes later, the flanker having returned following an 18-month absence through injury.
The Scarlets were much more competitive than they had been in the first half, but lacked a cutting edge.
Ulster similarly struggled to inject momentum into a performance that had become quite flat in the second half.
The inevitable introduction of the substitutes affected the impetus of a game that lacked any discernible continuity in any case.
The hosts had a couple of decent chances to kill off the Scarlets' resistance in the last ten minutes, but they were unable to finish them off.
The Scarlets were their own worst enemies at the end of the game, and suffered from poor indiscipline in the final few minutes.
The TMO thus ensured a perfect finish for the Belfast side when replacement Court got over the line from a few yards out. Jackson converted to seal a thoroughly deserved, if flawed victory for the Ravenhill club. Irish fans will hope that they have further cause for celebration before the weekend is over.
Tries: Jackson 2, Bowe, Court
Con: Jackson 3
Pen: Barkley 2
Ulster: 15 Jared Payne, 14 Tommy Bowe, 13 Darren Cave, 12 Stuart McCloskey, 11 Rory Scholes, 10 Paddy Jackson, 9 Ruan Pienaar, 8 Nick Williams, 7 Sean Doyle, 6 Roger Wilson, 5 Robbie Diack, 4 Johann Muller (capt), 3 John Afoa, 2 Rob Herring, 1 Callum Black.
Replacements: 16 Niall Annett, 17 Tom Court, 18 Ricky Lutton, 19 Lewis Stevenson, 20 Stephen Ferris, 21 Michael Heaney, 22 Craig Gilroy, 23 Ricky Andrew.
Scarlets: 15 Jordan Williams, 14 Kristian Phillips, 13 Gareth Maule, 12 Olly Barkley, 11 Frazier Climo, 10 Aled Thomas, 9 Gareth Davies, 8 Rob McCusker (capt), 7 John Barclay, 6 Josh Turnbull, 5 Johan Snyman, 4 George Earle, 3 Jacobie Adriaanse, 2 Kirby Myhill, 1 Phil John.
Replacements: 16 Darran Harris, 17 Rob Evans, 18 Shaun Hopkins, 19 Richard Kelly, 20 Sione Timani, 21 Aled Davies, 22 Josh Lewis, 23 Adam Warren.
Referee: Neil Hennessy (WRU)
Assistant referees: Gary Conway (Ireland), Gary Glennon (Ireland)
Television match official: Marshall Kilgore (Ireland)
Assessor: Jack Young (Ireland)
By Rory McGimpsey