Stradey Park, or Parc Stradey as it is signposted around the steel town, is steeped in the glorious rugby history accumulated down the years by this aristocratic club. Rugby lore does not greet you, hand outstretched, at the ramshackle old ground, it embraces you in a massive West Wales hug. Some welcome. Some hug.

While Harlequins were being welcomed, they were also being outrun, out-thought and outplayed. The scoreline at half-time was 19-3 to the Scarlets, who were by no means flattered by it. Chris Malone was kicking badly. Harlequins were being outscrummaged.

Llanelli were moving the ball quickly and looked dangerous whenever they attacked, which they did with abandon. Anyone who had said that the second half would be as good for Harlequins as the first half had been for the Scarlets would have been given some extremely odd looks indeed.

Yet at the end, it was Harlequins who celebrated. They made a remarkable comeback in which Danny Care and Ugo Monye scored tries and Malone kicked five penalty goals. The revival was sparked by incisive analysis and inspirational talking by John Kingston, the Harlequins head coach, who laid into his men at half-time, criticising them for allowing their opponents to run at them. He urged the Harlequins players to “get up and at their opponents - you're giving away far too much ball”. Harlequins also reminded themselves that not long ago, they had led 20-3 at half-time against London Irish - and lost. If it can be done to us, they must have thought, we can do it to them.

The Scarlets were shocked afterwards at the way their control of the match had been wrested away in the second half, when Care ran much more directly, and he and his team-mates were much more forceful. The Scarlets' concern was not alleviated by the prospect of going to Paris to play Stade Français in another pool four match this weekend.

“We've beaten ourselves again and that is disappointing,” Nigel Davies, the Scarlets head coach, said. “This side can play rugby, there is no doubt about that. We have got to learn to win the big games.”

Even three hours after the final whistle, Stephen Jones, the Scarlets fly half, could not work out what had happened. “It was a bit of a mystery,” he said, shaking his head.

Scorers: Scarlets: Tries: Stoddart (1min), M Jones (10). Penalty goals: S Jones 4 (25, 35, 44, 52). Harlequins: Tries: Care (59), Monye (70). Conversions: Malone 2. Penalty goals: Malone 5 (15, 46, 48, 71, 80+7). Scoring sequence: (Scarlets first): 5-0, 10-0, 10-3, 13-3, 16-3, 19-3 (half-time), 19-6, 19-9, 22-9, 22-16, 22-19, 22-26, 22-29. Scarlets: M Stoddart; D Daniel, R King (rep: R Higgitt, 69), G Evans, M Jones (rep: C Thomas, 75); S Jones, S Martens (rep: M Roberts, 62); I Thomas, M Rees (sin-bin, 58-68), K Meeuws, V Cooper (rep: N Thomas, 70), S Maling, S Easterby, G Thomas, D Lyons.

Harlequins: M Brown; C Amesbury, G Tiesi (rep: E Taione, 69), J Turner-Hall, U Monye; C Malone, D Care (rep: A Gomarsall, 78); C Jones, G Botha (rep: T Fuga, 54), M Ross, O Kohn (rep: G Robson, 54), J Evans, C Robshaw, W Skinner, T Guest (rep: N Easter, 54).

Referee: C Berdos (France).

Attendance: 8,236.