After last weekend's defeat to Glasgow, Ulster welcomed back five big names into their starting ranks, with Craig Gilroy reclaiming the number 11 jersey, and Rory Best, John Afoa, Stephen Ferris and Chris Henry all returning upfront.

Ravenhill was also buoyed by the inclusion of a fit-again Ruan Pienaar on the bench, with the in-form Paul Marshall continuing on as the province's starting scrum half.

Ulster were under pressure straight from the kick-off, and although they looked initially to have played themselves out of trouble, a careless pass from Pedrie Wannenburg gifted possession to Sean Lamont well inside the home 22, and the Scotland wing had an elementary dash into the corner for a second minute try.

The conversion attempt from the experienced Stephen Jones veered off target, however, and stung by the concession of that try Ulster needed an immediate reaction.

Humphreys watched his eighth minute penalty attempt miss the posts, and chances proved scarce as the game edged towards the second quarter.

The Scarlets then proceeded to pile on a second coat of misery in the 19th minute when Vilami Iongi touched down in the right corner after a swift change of direction at the breakdown had caught Ulster off guard.

A second missed conversion followed, and almost before the Scarlets had time to draw breath, Humphreys kicked over a penalty to cut the gap to 10-3.

The Scarlets were reduced to 14 men on the half hour with full-back Daniel Evans pulled up for deliberately interfering with Humphreys' arm as he readied himself to throw a pass.

Three minutes later Ulster were back within touching distance. An inspirational solo run on the right from Marshall got the province firing at last.

He darted through a hole at the breakdown and then gobbled up his own crafty kick before being hauled down just short of the try-line.

Ulster recycled quickly and moved the ball out to the left for Ferris to carry strongly and force his way over the line. Humphreys' conversion attempt was narrowly off target, but Brian McLaughlin's men were right back in it.

The situation could have improved further still before half-time when Darren Cave looked to have broken free on the right wing, but referee Alain Rolland called play back for an apparent forward pass from Nevin Spence. Nevertheless, Ulster ran off at the interval with their tails up, and only two points in arrears (10-8).

Marshall's talismanic performance continued as the second half opened, a clever dink into touch deep in Scarlets territory putting the visitors under pressure.

After Dan Tuohy had won possession back among a melee of bodies, a high tackle on ball recipient Spence gave Humphreys a simple penalty in front of the posts.

A second penalty followed moments later from a similar position, and Ulster's indefatigable spirit had suddenly propelled them into a 14-10 lead.

Humphreys extended the hosts' advantage in the 59th minute with an expertly-struck penalty from distance - his fourth of the encounter - and with Pienaar entering the fray on the hour mark, the Ulstermen soon struck the killer blow.

A string of quick-fire passes across the line from left to right again freed up Ferris to brilliantly barrel over for his second try. Humphreys applied the icing and left the Scarlets trailing by 24-10

Despite a yellow card for replacement prop Adam Macklin in the 72nd minute, Ulster defended manfully as the Scarlets, camped in the opposition 22, looked to salvage something from the game.

Although league debutant Kieran Murphy slid over and Jones converted to secure a losing bonus point for the visitors, Ulster had enough in the tank, and even ended the clash in possession in Scarlets territory.

The victory is a much-needed fillip for McLaughlin's charges as they try to make up lost ground in the RaboDirect PRO12, and also gives them a timely boost ahead of next week's crucial Heineken Cup collision with Aironi.