Daniel Brendon fails to get past Llanelli's Dafydd James (left)
Reivers 13 (13)
Pens: MacRae (2)
Scarlets 19 (10)
Cons: C. Thomas
Pens: C. Thomas (4)
Llanelli Scarlets edged out Reivers at Netherdale, as Simon Danielli's hopes of a Scotland recall were in tatters after he suffered a smashed cheekbone.
Winger Danielli was rushed to hospital after grabbing a touchdown for the Border Reivers and will now be sidelined for several weeks.
The Scarlets reduced the deficit before the break when Jon Mills crossed for a try, converted from Ceiron Thomas.
And Thomas then led the visitors to victory as he landed three penalties.
Reivers made the early running, but could not turn pressure into instant points.
There was a setback for the Scarlets when Kiwi prop Craig Dunlea - formerly with Hawick - limped off with a knee problem.
Despite the front-row re-jig Scarlets found a rhythm and they edged ahead with a well-struck penalty by Thomas in the wake of a Steve Jones challenge on Regan King.
Borders had a great opportunity to seize the initiative as Jones sent the visiting defence into a panic with a beautifully weighted chip.
But the opportunity was lost when Calum MacRae spilled the ball virtually underneath the crossbar.
MacRae made quick amends by slotting a penalty, which inspired the Scots to create a top-notch touchdown.
Jones snapped up a loose ball inside his own half before freeing Garry Law. He acted as the perfect link to give Danielli the time and space to gallop to the target from 45 metres out.
MacRae added the extra points, but the joy was diluted when Danielli was taken off injured and was replaced by Bryan Rennie.
The stunned Scarlets regrouped before the break and they reduced the deficit with a score by backrower Mills at the end of a forward surge.
Thomas converted, but there was still time for the Reivers to haul themselves back in front as MacRae landed his second penalty to snatch back the lead for the home players.
The Scarlets had the better of the exchanges after the restart and Thomas was on target with a 50th-minute penalty to tie the scores and set up a tense finale.
He struck again midway through the half to give the Welshmen the edge, and although Reivers battled on, he sealed victory with just seconds remaining with his fourth penalty.
Borders: MacRae; Danielli, MacDougall, Law, Daniel; Jones,
McKearchar; Grant, Scott, Douglas, Hamilton, Palepoi, Dalziel,
Replacements: Rennie for Danielli (26),
Townsend for Jones (75), Cross for Grant (52),
Newlands for Dalziel (65).
Not Used: Crombie, Vernon, Chrystie.
Llanelli Scarlets: B. Davies; James, King, Watkins, Daniels;
C. Thomas, Stuart-Smith; I. Thomas, Gravelle, Dunlea, Afeaki,
A. Jones, Mills, N. Thomas, Bater.
Replacements: G. Evans for King (63), Owen for Gravelle (78),
Manu for Dunlea (3).
Not Used: Reed, Cooper, L. Davies, Stoddart.
Ref: Olan Trevor (Munster).