Botica boots Quins to victory
Substitute Ben Botica kicked a 78th-minute penalty to keep alive Harlequins' European campaign and give them a consolation prize of an Amlin Challenge Cup quarter-final place.
Quins, already out of Heineken Cup last-eight contention, moved into the Amlin knockout phase along with Northampton and Gloucester by prevailing in west Wales to finish as runners-up in Pool 4.
Wales centre Scott Williams looked to have claimed the decisive touchdown, which followed earlier Scarlets tries by scrum-half Gareth Davies and flanker Aaron Shingler, while Rhys Priestland kicked a penalty and conversion.
But Quins scored three tries of their own - full-back Mike Brown, wing Ollie Lindsay-Hague and scrum-half Karl Dickson crossing - and Nick Evans booted two conversions during a game when the visitors led 14-7 and 19-15 before they finally sealed a victory which earned an Amlin last-eight clash away to Stade Francais in early April.
The Scarlets started the quicker and announced their intentions by stunning Quins with a superb fifth-minute try that had is origins deep inside their own half.
Wing Jordan Williams prospered from a Priestland long pass by standing up the Quins defence, and after number eight Rob McCusker acted as link-man, Davies sprinted 30 metres to score.
Priestland converted, and the Scarlets were off and running in pursuit of an Amlin place before Shingler gave Quins a temporary one-man advantage when he received a yellow card for a dangerous charge on Tom Guest.
It was poor discipline by the Wales Six Nations squad member, and Quins punished the Scarlets by responding through a Brown touchdown created by Evans' approach work, and the New Zealander's conversion made it 7-7.
A torrential downpour made conditions treacherous midway through the first-half, but Quins - and Brown in particular - were determined not to be knocked out of their stride, with a second Quins try arriving after 28 minutes.
Slick handling stretched the Scarlets defence, and it was Brown's deft inside pass that enabled Lindsay-Hague to cross unopposed before Evans' conversion established a seven-point advantage.
Back came the Scarlets, though, and after a Priestland penalty narrowed the deficit, Shingler scored an opportunist try that left Quins one point behind at half-time.
Quins appeared to be in little danger at a set-scrum near their own line, but when the ball squirted free from the base, Shingler reacted quickest and put his hand on it for a try that referee Jerome Garces awarded following consultation with television match official Jean-Marie Piraveau.
The second-half started at breakneck pace, as Quins briefly regained the lead before it was snatched back from them with the lead changing hands for a fourth time.
Dickson showed his pace and elusiveness to breach the Scarlets defence after 45 minutes, but Quins were then undone by another Jordan Williams-inspired Scarlets breakout that ended with Scott Williams crossing from close-range.
It was thrill-a-minute rugby as both teams were prepared to back their handling skills and put an emphasis on attacking rugby, rather than a safety-first kicking game adopted by so many teams.
Both sides had worked themselves almost to a standstill entering the final 10 minutes, but Quins, driven on by England captain Chris Robshaw, were not to be denied.