A last-minute penalty by Ronan O'Gara saw Munster prevail 18-16 at the Parc y Scarlets on Friday, after the home side had nearly pulled off a superb Magners League fightback.
After gaining a penalty try four minutes into injury-time, after Donncha O'Callaghan was sin-binned, the Scarlets thought they were on course for victory.
But O'Gara, captaining Munster in place of the rested Paul O'Connell, had other ideas.
Before the end, Scarlets' replacement Ceiron Thomas had a desperate, last-gasp drop-goal attempt charged down as the home side had to settle for a losing bonus point.
It was a night full of drama after the kick-off looked set to be put back after a rush-hour crash on the M4.
And although Munster made it through the traffic, the chaos caused a change of referee, with Welsh Rugby Union official James Jones taking over the whistle from Scotsman Peter Allan, who was caught in a tailback.
Allan missed out on a bit of history at the new stadium which has taken over from Stradey Park, where the Llanelli and Scarlets played their rugby for the last 129 years until last month.
The first points at the new venue came courtesy of O'Gara, but Rhys Priestland levelled it up after 23 minutes with his own penalty and then Munster centre Lifeimi Mafi received a yellow card.
But it was very much Munster's half as they scored two tries in the last eight minutes.
First, wing Ian Dowling evaded some poor defending by wing Matthew Jacob and Morgan Stoddart, who had been released from the Wales squad.
And on the stroke of half-time a strong Munster scrum on the five-metre line allowed number eight Denis Leamy to squeeze over for a converted try to give the league leaders a 15-3 interval lead.
Despite a poor set-piece the Scarlets rallied in the second half and were much the better side, but they could not make the O'Callaghan sin-binning count.
For the Scarlets:
Try: Penalty try
Pens: Priestland 3
Tries: Dowling, Leamy
Pens: O'Gara 2
Scarlets: 15 Morgan Stoddart, 14 Darren Daniel, 13 Regan King, 12 Gavin Evans, 11 Jon Davies, 10 Rhys Priestland, 9 Sililo Martens, 8 David Lyons, 7 Simon Easterby (c), 6 Nathan Thomas, 5 Dominic Day, 4 Vernon Cooper, 3 Kees Meeuws, 2 Ken Owens, 1 Iestyn Thomas.
Replacements: 16 Deacon Manu, 17 Mahonri Schwalger, 18 Phil John, 19 Rob McCusker, 20 Johnathan Edwards, 21 Gavin Cattle, 22 Ceiron Thomas.
Munster: 15 Paul Warwick, 14 Doug Howlett, 13 Keith Earls, 12 Lifeimi Mafi, 11 Ian Dowling, 10 Ronan O'Gara, 9 Tomas O'Leary, 8 Denis Leamy, 7 Niall Ronan, 6 Donnacha Ryan, 5 Mick O'Driscoll, 4 Donncha O'Callaghan, 3 Tony Buckley, 2 Frank Sheahan, 1 Marcus Horan.
Replacements: 16 Denis Fogarty, 17 Federico Pucciariello, 18 James Coughlan, 19 John O'Sullivan, 20 Peter Stringer, 21 Barry Murphy, 22 Anthony Horgan.
Referee: Peter Allan (Scotland)
Touch judges: James Jones (Wales), Steve Edwards (Wales)