There was a new look to both sides as they lined out at Parc y Scarlets. The hosts included recent signings Sean Lamont, Rhys Thomas and Richie Pugh in their starting line-up.

Leinster handed a competitive debut to Australian centre Shaun Berne and the likes of scrum half Chris Keane and flanker Kevin McLaughlin were given a chance to impress.

The Scarlets, beaten by Leinster in their last three meetings, got off to an encouraging start as Scottish winger Lamont burst through for a sixth minute try.

Nigel Davies' men spread the ball out to the left where the Leinster defence was caught off guard and Lamont, running from deep, was able to shoot through a gap and gallop over from 40 metres out.

Number 10 Rhys Priestland added the conversion and the Scarlets thwarted Leinster's immediate attempts to reply, picking up two turnovers.

But when a penalty was moved forward for back chat, just outside the Scarlets' 22, Jonathan Sexton stepped up to kicking Leinster's opening points.

Sexton increased his influence as the Leinster forwards began to command the breakdown.

On the quarter hour mark, the out-half hung up an inviting crossfield kick for Isa Nacewa who gathered it well within sight of the try-line - but Scarlets full-back Daniel Evans snuffed out the danger with a textbook tackle.

Leinster's confidence was growing, though, and after their forwards had muscled back to within five metres of the line, a try always seemed likely.

They battered away and drew in defenders before a quick switch out to the right ended with Berne's well-placed pass putting Girvan Dempsey over unchallenged in the corner.

Sexton kicked the conversion for good measure and unforced errors from Priestland and Evans showed signs of anxiety from the Scarlets.

The impressive McLaughlin forced a penalty, midway through the half, which Sexton converted for 13-7 and the Leinster blindside blocked down a drop goal attempt from Priestland soon after.

A frustrated Pugh was sin-binned for killing Leinster ball at a ruck, with Sexton pinging over his third successful penalty.

The Scarlets' woes deepened three minutes later when dangerous play at a ruck resulted in prop Rhys Thomas receiving a yellow card.

Thomas went in recklessly at a ruck, catching a prone Shane Horgan with his head and the Leinster winger did well not to react to the incident.

Referee Neil Paterson was a busy figure as the packs went toe-to-toe and Leinster prop Stan Wright was the third player to be sin-binned in quick succession, walking for a shoulder charge challenge on David Lyons.

While the hosts were down to 13 men, Leinster could not transfer pressure and a territorial advantage into points and that proved crucial as the game wore on.

Indeed, Davies' side succeeded in absorbing anything Leinster could throw at them before the break and Priestland knocked over a morale-boosting penalty with the last kick of the half, making it 16-10.

The second half had a scrappy feel to it, with the yellow cards understanably having an effect on the flow of the game.

Both Nacewa, who impressed throughout under the high ball, and Shane Jennings went close to scoring Leinster's second try.

Jennings just lost control of the ball as he stretched for the whitewash. Television match official Tony Rowlands confirmed that the Ireland flanker had failed to get downward pressure.

There was a lack of penetration from both sides as the clock hit the hour mark - but then, almost out of nothing, the Scarlets closed the gap to 16-15.

Jonathan Davies, who had an excellent final quarter, made a surging run through the middle, the Scarlets swept the ball clear from the ruck on the Leinster 22 and skipper Mark Jones brilliantly danced along the right touchline and passed back inside for replacement prop Phil John to collect and bound over for a well-executed try.

Priestland missed the conversion, but the Scarlets' tails were suddenly up and the home support really increased the noise levels.

They roared their approval on 64 minutes when Leinster replacement flanker Sean O'Brien was sin-binned for holding onto the ball on the deck as the Scarlets raided through onto a kick ahead from Dafydd Jones.

Dempsey was left bloodied and bruised in the scramble as the Welsh region piled forward. With O'Brien in the bin, Priestland landed the resulting penalty for an 18-16 lead.

With enough time left, Leinster had their chances to reply. Horgan engineered some space on the right and disciplined defence was called for from the Scarlets as the visitors edged closer to the try-line.

But Sexton and replacement full-back Niall Morris both got isolated in good attacking situations and while Priestland also missed a late drop goal attempt, the Scarlets had done enough to survive and post their first win of the league run.