The Scarlets fought back from a 10-16 half-time deficit to record an opening day 18-16 win over Leinster in the Magners League on Saturday.
Tries from Sean Lamont and Phil John kept the Scarlets in a match they seemed destined to lose before Rhys Priestland gave his side the lead with a 71st minute penalty.
And Leinster, minus six British Lions including Brian O'Driscoll, must have wondered how they lost a game they dominated in both possession and territory.
New signing Lamont grabbed the first try of the Scarlets' new season after just six minutes, and a memorable score it was too.
The Scotland wing cruised past four would-be tacklers to go over for the try, converted by Priestland.
But after Jonathan Sexton cut the deficit with a penalty goal on 13 minutes Lamont was caught out of position as wing Isa Nacewa caught a cross kick and headed to the corner. He touched the ball down but was forced into touch by Daniel Evans.
Leinster made amends on 19 minutes as Girvan Dempsey went in down the right after pressure had developed an overlap.
The visitors' lead increased from 10-7 to 16-7 with two more Sexton penalties, the second coming after Richie Pugh was sin-binned for using his hands in a ruck.
Four minutes later the Scarlets were down to 13 men after suffering a second yellow card when Rhys Thomas was sent to the cooler for dangerous play at a ruck.
In injury time referee Neil Paterson's cards were out again this time to send Leinster prop Stan Wright to the bin for a reckless challenge on David Lyons.
And eight minutes into time added on Priestland slotted over a penalty to cut Leinster's interval lead to 16-10.
Twelve minutes into the second half the Irishmen thought they had scored their second try when Shane Jennings appeared to get the ball down on the line, but the TV match official ruled it out.
Against the run of play it was the Scarlets who registered the first score of the second half after 25 minutes.
Jonathan Davies made the initial break into the Leinster half before Mark Jones put replacement prop John over.
Though Priestland missed the conversion he put over a penalty goal five minutes later which put the Scarlets into a two point lead.
The penalty came after Leinster's replacement back-rower Sean O'Brien was sin-binned for a professional foul.
In injury time Priestland was wide with a drop-goal attempt which added pressure to the Scarlets' victory charge.
But they held on despite the referee adding on eight minutes of injury time.
For the Scarlets:
Tries: Lamont, John
Pens: Priestland 2
Pens: Sexton 3
Yellow cards: Pugh (30, Scarlets), Thomas (33, Scarlets), Wright (38, Leinster), O'Brien (64, Leinster)
Scarlets: 15 Daniel Evans, 14 Sean Lamont, 13 Rob Higgitt, 12 Jonathan Davies, 11 Mark Jones (capt), 10 Rhys Priestland, 9 Martin Roberts, 8 David Lyons, 7 Richie Pugh, 6 Simon Easterby, 5 Dominic Day, 4 Lou Reed, 3 Rhys Thomas, 2 Ken Owens, 1 Iestyn Thomas.
Replacements: 16 Phil John, 17 Emyr Phillips, 18 Deacon Manu, 19 Vernon Cooper, 20 Dafydd Jones, 21 Lee Williams, 22 Dan Newton.
Leinster: 15 Girvan Dempsey, 14 Shane Horgan, 13 Fergus McFadden, 12 Shaun Berne, 11 Isa Nacewa, 10 Jonathan Sexton, 9 Chris Keane, 8 Stephen Keogh, 7 Shane Jennings, 6 Kevin McLaughlin, 5 Malcolm O'Kelly, 4 Leo Cullen (c), 3 Stan Wright, 2 John Fogarty, 1 Cian Healy.
Replacements: 16 Bernard Jackman/Jason Harris-Wright, 17 Mike Ross, 18 Devin Toner, 19 Sean O'Brien, 20 Paul O'Donohoe, 21 Simon Keogh, 22 Niall Morris.
Referee: Neil Paterson (Scotland)