Ulster would face Perpignan or Toulon in the semi-finals if they were to beat Northampton.
Perpignan replied through Adrien Plante, Ovidiu Tonita and Damien Chouly but the French side fell just short.
Beaten 52-14 in Perpignan in June, they started well, opening the scoring when Hicks kicked a penalty.
Perpignan took the most direct route to strike back within five minutes with a try for Guirado.
Roussillon sits to the west of Perpignan but culturally, it lends itself more to Catalonia than France.
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The Scarlets bossed the early stages but found themselves trailing on the scoreboard as Perpignan countered with glee.
They include current Test stars James Hook and Lee Byrne who are joining Perpignan and Clermont Ferrand respectively.
"I've been making a few phone calls, and if we win I'll know where to celebrate in Perpignan!"
The fly-half, who averages 20 points a game against England, next week starts a six-month sabbatical with Perpignan.
Hook is joining Perpignan, Byrne is heading to Clermont Auvergne and Henson has already moved to Toulon via Saracens.
Gross' ban rules him out of next weekend's Heineken Cup clash against Perpignan, as well as important league games.
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In his Perpignan contract, Hook is guaranteed to be released to Wales for all pre-World Cup training and matches.
Turnbull was again involved, stealing a line-out that allowed the ball to be punted deep into the unmanned Perpignan 22.
Instead, the Aussie playmaker produced another sensational performance to complete a wonderful week in Manchester for the men from Perpignan.
Once west of Perpignan, the landscape starts to resemble parts of New Zealand, with crystal-clear, robin-egg-blue skies and snow-covered peaks.
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Ibanez began his career in his hometown of Dax before moving on to Perpignan, Castres and then to Saracens in 2003.
Porical struck a penalty to reduce Perpignan's deficit to 26-15 at half-time, but the Scarlets were soon back on the try trail.
Bosc again made no mistake with the boot in front of just under 10, 000 spectators at the Stade Gilbert Brutus in Perpignan.
Donkin says the intense summer heat could make visits to their home grounds in Perpignan, Narbonne and Figueres in northern Spain a daunting prospect.
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Mallinder made a raft of changes as Northampton pushed forward for a bonus-point try, but were thwarted as Perpignan firmed up their flimsy defence.
Lloyd White pulled one back before two in three minutes from Setaimata Sa and Damien Blanch appeared to have settled the outcome in Perpignan.
"It is not going too well, " he admits, but he is looking forward to some individual tuition once he arrives in Perpignan next week.
The defeat compounds a disappointing European campaign for French champions Perpignan, who are still winless in the Heineken Cup against English teams away from home.
"We've built up quite a rivalry with Leicester in our short existence, " said Humphreys, who then face Perpignan and a double header with Benetton Treviso.
But one pluspoint is that, although heading for Perpignan this week, Millard will not play in Saturday's match against Wakefield at the Gilbert Brutus Stadium.
Joe Bearman crossed after half-time but Henry Tuilagi replied for Perpignan.
Perpignan play Toulon and Biarritz host Toulouse in two all-French ties.
If the Scarlets thought the game was won, however, Perpignan soon gave evidence that there was still much more to come from a thrillingly open game.
What we wanted to do was go and make a statement in France, there in Perpignan and for long periods I thought we were going to.
It was not enough to overhaul Perpignan as the French side went through as group winners after they also sealed a bonus-point victory, 37-5 against the Scarlets.
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