The Welsh side, without the injured British Lions number eight Scott Quinnell and a lowly ninth in the table before the game, showed plenty of spirit to overcome Leinster’s 19-10 half-time lead.

Flanker Jonathan Mills made his debut for Llanelli and went on to play a key role his side’s first try after just five minutes.

Mills surged into the heart of the Leinster cover and when the ball was spun along the back line, centre Matthew Watkins cut through to score under the posts.

Leinster, without 11 of their international stars, went on to dominate the remainder of the half.

Kiwi fly-half David Holwell was the fulcrum, kicking four successive penalties and a conversion of prop Ricky Nebbett’s 26th minute try from a short-range lineout.

Leinster should have been further ahead at the interval, but were guilty of missing a couple of golden opportunities late in the half.

After sending Scarlets flanker Gavin Thomas to the sin bin, Scottish referee Andy Ireland then dispatched Leinster prop John Lyne.

Gareth Bowen then missed two more penalties which would have closed the gap.

A rare Leinster mistake then gifted the Scarlets their chance.

A floated David Holwell pass bounced invitingly into the arms of Tongan speedster Aisea Havili and he had the gas the race 60 yards to the line.

A fifth Holwell penalty took it back to 22-17, but back came the Scarlets with a fine try created and finished by full-back Barry Davies on 71 minutes.

Bowen’s conversion put the Scarlets back ahead and in the frantic closing minutes they were able to hold out for only a third league win of the season.

Leinster now have to be satisfied with the consolation of a losing bonus point.