The Irish side moved further clear at the top of the RaboDirect PRO12 table with a comprehensive 47-17 win but it was North's injury which would most concern Wales interim head coach Rob Howley ahead of the Six Nations.

The wing was replaced in the second half and stretchered off wearing a neck brace with Ulster leading comfortably.

Second half scores from Robbie Diack and giant No. 8 Nick Williams saw Ulster pull clear before Andrew Trimble's score, a penalty try and replacement Neil McComb secured a bonus point win.

Scrum half Ruan Pienaar controlled the game, kicking expertly out of hand and from the floor as his three penalties saw Ulster lead 9-3 at half time.

And they ran riot after the interval, putting the Scarlets to the sword with five tries. Josh Turnbull and Scott Williams replied for the Welsh side but it was too little too late.

Both sides made mistakes in a scrappy opening, Aled Thomas kicking out on the full while his opposite number Paddy Jackson knocked on inside his own 22.

The Scarlets made the most of Jackson's error and when the Irish side were penalised for being off their feet at a ruck, Thomas' low penalty gave the Scarlets a 3-0 lead.

Ulster's attacking play has seen them tear opposition defences to pieces on a regular basis this season and their danger was all too obvious in the early exchanges.

The final pass did not quite go to hand though and the Scarlets' tactical kicking pinned the home side back inside their own half. Following another chip through, Thomas was given a chance to add a second penalty after Rob Herring overthrew an Ulster line out. The kick never looked like being successful though as the fly half dragged it wide of the left hand upright.

Pienaar soon levelled things up with a penalty of his own before the game began to open up. A break from Jonathan Davies saw the Wales centre clean through before Thomas brilliantly collected a Jackson cross kick with three Ulster backs waiting to pounce outside him.

It was refreshing to see both sides testing the opposition defence, Irish international Craig Gilroy breaking through before Williams burst round the side of a ruck to win a penalty.

Pienaar's metronomic boot did the rest as Ulster dominated the rest of the half, stretching the Scarlets from touchline to touchline. A try failed to materialise though and they had to contend with another Pienaar penalty for a 9-3 interval lead.

Without a first half score, Ulster soon made amends with a try minutes after half time. Williams' physical presence saw him find space and brilliantly offload to Herring. The hooker drew the last defender and offloaded to Diack who ran in with ease. Pienaar added the conversion and a fourth penalty soon after and at 19-3 down, the Scarlets faced an uphill battle.

With ball in hand, Ulster looked dangerous every time they came forward with Williams the main threat. The Kiwi again burst through, just failing to find replacement Paddy Wallace with his offload. It mattered little though as the No. 8, who has made the most carries in the PRO12 so far this season, burst over from close range following a quick tap penalty.

Pienaar easily converted the score as Ulster moved out of sight.

Things then went from bad to worse for the Scarlets when North was stretchered off.

They refused to give up though and got their reward when Turnbull bulldozed over. Thomas converted but Trimble's converted score, a penalty try and McComb's late effort sealed their fate in a hectic last 10.

Replacement Williams went over for a consolation on the final whistle but Ulster were deserving winners.