Ireland winger Denis Hickie's two tries could not prevent Llanelli moving back to the top of the Magners League after holding off a spirited second-half Leinster fightback to win 33-21 at Stradey Park.
The Welsh side led 27-0 after a sparkling opening salvo but Leinster, without most of their Ireland stars, fought back strongly after the break.
The down side for the Scarlets, however, was what looked a serious arm injury suffered by star scrum-half Dwayne Peel early in the second half.
But as they turn their attention to next week's EDF Anglo-Welsh Cup clash with Harlequins, they will be sitting pretty four points clear of Ulster at the top of the table.
Llanelli crossed for two tries inside the opening four minutes and had notched up their four-try bonus point with just over a quarter of the match gone.
With the sun beating down at Stradey Park, the Scarlets played some spectacular stuff early on to stun the Irish side, who had been delayed arriving at the ground because of traffic on the journey from their hotel.
The had only had one touch of the ball, a dropped kick-off by flanker Stephen Keogh, before watching the Scarlets touch down for their first try by Dafydd James.
Tongan second row Inoke Afeaki followed soon after following some superb handling involving forwards and back.
James' second score was all down to a slick three-quarter line with Kiwi centre Regan King making the initial break, feeding full-back Ceiron Thomas, who off-loaded just short of the line.
A Jones conversion and then penalty from straight in front made it 20-0 to the home side with barely 15 minutes on the clock.
And it got better for the home fans soon after when King cantered through some non-existent Leinster defence for the Scarlets' fourth.
Leinster were staring down the barrel of a record hammering but Hickie managed to pick off a stray Peel long pass and race 60 metres unopposed for his side's lone strike of a hugely entertaining first period.
Hickie scored a second after smart work around the fringe, but Peel suffered his injury in the process and, with Wales coach Gareth Jenkins a concerned onlooker, it did not look good for the Lions star.
It needed some desperate Scarlets defence to keep Hickie out for his third soon after before Jones settled the home side with a penalty from straight in front.
But Leinster kept coming back and a quick tap by lively replacement scrum-half Chris Whitaker saw lock Trevor Hogan cross on 64 minutes.
England flanker James Haskell insists he will be pushing as hard as possible to be back from a toe injury in time to make his case for a spot in Eddie Jones' side looking to defend their RBS 6 Nations title next year.