Harlequins 29 Scarlets 24
Harlequins gave themselves the best possible chance of landing a home Heineken Cup quarter-final by clinching a bonus-point victory over the Scarlets today.
Dean Richards' men ran in four tries - from Chris Robshaw, George Robson, James Percival and Tom Williams - in a dominant performance at The Stoop.
The Scarlets caused Quins a brief scare with quickfire tries in the second-half from Wales internationals Morgan Stoddart and Matthew Rees.
And Gavin Evans earned the Scarlets a losing bonus point with a last-minute try under the posts.
But Quins had already secured themselves maximum points and will now wait anxiously in the hope of being confirmed as one of the top four seeds for the knockout stages.
Harlequins chief executive Mark Evans confirmed after the Guinness Premiership game at Twickenham over Christmas that they would play a home quarter-final at The Stoop.
Despite defeat in stormy Ulster last weekend, Quins were already confirmed as Pool Four winners by virtue of Stade Francais' defeat to the Scarlets.
They needed a bonus-point victory to maximise their chances of a home quarter-final and set about claiming it with a ferocious start.
The Scarlets withstood a 10-minute bombardment and actually took the lead with a penalty from Stephen Jones, but it came from their only decent attack of the half.
Normal service was swiftly resumed as Chris Robshaw's rampaging run after a break from winger Tom Williams carried Quins deep into Scarlets territory again.
Dafydd Jones was penalised for holding on, but so solid was Quins' attacking platform that captain Will Skinner spurned a penalty shot at goal in search of the opening try.
The Quins pack was dominant and set a perfect attacking platform for the likes of Ugo Monye, who was in electric form before limping off with a back problem, and full-back Nick Evans.
Skinner's decision came to nothing initially but Quins remained camped in the Scarlets 22 and Nick Evans finally put them on the scoreboard.
It was scant reward for 21 minutes of virtually unbroken dominance - but before the half hour was up Quins had raced into a 15-3 lead and were halfway to securing that try bonus.
The impressive Gonzalo Tiesi claimed the restart and was driven 20 metres to halfway, Nick Easter crashed over the gain-line and then Robshaw combined brilliantly with Tom Williams to score in the corner.
Williams cut in off the right wing onto a pass from Robshaw and spun out of a tackle to make 30 metres before pushing the ball back for the Quins flanker, who crashed over the line.
Quins kept coming in waves and almost scored another straight from the kick-off when Evans' deft dummy created space for fly-half Chris Malone, but his lack of pace was exposed and Regan King hauled him down just short of the line.
Quins secured a turnover at the five-metre scrum and remained camped in the Scarlets 22, sucking in defenders to create space for Robson to score the second.
Monye left the fray after 35 minutes having apparently injured his back while reclaiming an up-and-under and was replaced by the exciting Quins academy winger Charlie Amesbury.
Quins almost worked a third try after Evans turned a scruffy ball into a chance but Jordan Turner-Hall's delicate flick out wide to Williams was judged just forward.
There was little change to the momentum after the interval and Quins duly chalked up their third try as James Percival drove over following Easter's break from the back of another powerful five-metre scrum.
The Scarlets, having been on the receiving end for the best part of an hour, burst into life and scored twice in quick succession to put the frighteners up Harlequins.
Wales full-back Morgan Stoddart, on as a half-time replacement for Ceiron Thomas, finished off a slick attacking move under the posts before hooker Matthew Rees charged over the line.
Quins almost stole Rees' lineout throw but the tap-down missed Danny Care and the Wales hooker regathered the ball and fended off three defenders to score.
From nowhere, the Scarlets had recovered to within five points. Dean Richards responded by sending on Tom Guest - and the England prospect made an immediate impact as Quins sealed their bonus point.
With his first touch of the ball Guest galloped through the Scarlets line, brushing defenders aside. Quins spread the ball right and Evans sent Williams over in the corner.