The Northern Irish province were excellent in the first half and deservedly went into the break 13-10 in front via Jacob Stockdale and Henry Speight tries.
Rhys Patchell’s penalty and Steff Evans’ score had given the home side a two-point buffer, but they struggled for rhythm and those frustrations continued in the second period.
Will Addison punished their inadequacies by crossing the whitewash after the interval and, although Evans gave the Welshmen hope, Marcell Coetzee’s effort sealed the victory, even though Dan Davis responded late on.
Wayne Pivac’s men went into this game in the same situation as last year having lost their opening two matches in the competition. The Welsh region brilliantly responded to those defeats, winning four games in a row and eventually qualifying for the semi-finals, where they succumbed to Leinster.
The Scarlets needed a similar miracle this season and they started well, regaining the kick-off and earning a penalty, which Patchell converted for a 3-0 advantage, but they were ultimately not good enough on Friday night.
Ulster looked dangerous with ball in hand throughout and Addison almost set up a try early on as his neat grubber through was collected by Speight. Although the wing was eventually halted and the move broke down, the hosts infringed and John Cooney restored parity.
Dan McFarland’s charges then put together a brilliant move and Addison was once again to the fore. The Ireland international evaded the attentions of Jonathan Davies before providing some space to Stockdale, who duly finished superbly.
To the Welsh region’s credit, they responded excellently and regained the lead as Evans crossed the whitewash from close range, but Ulster were proving particularly obstinate opposition.
They pressurised the hosts’ rearguard and, with the defence lacking numbers on the blindside, Speight touched down in the right-hand corner.
Scarlets’ issues remained after the interval and the visitors took advantage, going over for the third time when Addison’s brilliant line ended in him scoring under the posts.
Pivac’s charges looked to hit back and they got themselves to within five metres out, but brilliant defence, particularly from Ireland captain Rory Best, initially relieved the pressure.
However, the Welshmen continued to attack and were eventually rewarded through Evans, who benefited from Johnny McNicholl’s wonderful piece of skill.
Unperturbed, Ulster got their hands on the ball once more, showed patience and Coetzee finished to seal an excellent result at last season’s semi-finalists, despite Davis’ late consolation.
Tries: Evans 2, Davis
Cons: Patchell 2, Jones
Tries: Stockdale, Speight, Addison, Coetzee
Scarlets: 15 Johnny McNicholl, 14 Tom Prydie, 13 Jonathan Davies, 12 Kieron Fonotia, 11 Steff Evans, 10 Rhys Patchell, 9 Gareth Davies, 8 Uzair Cassiem, 7 James Davies, 6 Will Boyde, 5 David Bulbring, 4 Lewis Rawlins, 3 Samson Lee, 2 Ken Owens (c), 1 Rob Evans
Replacements: 16 Ryan Elias, 17 Wyn Jones, 18 Werner Kruger, 19 Steven Cummins, 20 Dan Davis, 21 Kieran Hardy, 22 Dan Jones, 23 Hadleigh Parkes
Ulster: 15 Louis Ludik, 14 Henry Speight, 13 Will Addison, 12 Stuart McCloskey, 11 Jacob Stockdale, 10 Billy Burns, 9 John Cooney, 8 Marcell Coetzee, 7 Jordi Murphy, 6 Sean Reidy, 5 Kieran Treadwell, 4 Iain Henderson, 3 Marty Moore, 2 Rory Best (c), 1 Eric O’Sullivan
Replacements: 16 Rob Herring, 17 Kyle McCall, 18 Tom O’Toole, 19 Matt Rea, 20 Nick Timoney, 21 David Shanahan, 22 Johnny McPhillips, 23 Darren Cave
Referee: Alexandre Ruiz (France)
Assistant referees: Alexandre Ruiz (France), Cedric Marchat (France)
TMO: Eric Briquet-Campin (France)