Thirty-year-old Parks, who has four Wales caps, insists he has nothing to prove to his former employers, despite struggling to establish himself in the Perpignan side last year.
The Perpignan right winger hacked a loose ball 70m down the pitch and seemed certain to score, but Geraghty's outstretched boot somehow cleared the ball from under Plante as he prepared to apply the necessary downward pressure.
Turnbull was again involved, stealing a line-out that allowed the ball to be punted deep into the unmanned Perpignan 22.
The Scarlets go to Perpignan on Sunday whereas the Tigers host Italian side Benetton Treviso at Welford Road, giving them a major opportunity to underline their European credentials.
Scarlets scrum-half Martin Roberts was robbed as he went to pass from the base of a ruck and Perpignan spread the ball left towards Candelon, the wing kicking ahead and following up to gather and score.
Gareth Wyatt scored an early try for the Welsh, but Perpignan led 16-5 at the break through Guilhem Guirado's try and 11 points kicked by Cedric Rosalen.
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.
Instead, the Aussie playmaker produced another sensational performance to complete a wonderful week in Manchester for the men from Perpignan.
Lloyd White pulled one back before two in three minutes from Setaimata Sa and Damien Blanch appeared to have settled the outcome in Perpignan.
Two more penalties from the reliable boot of Rosalen handed Perpignan a 16-5 lead at the break, but again it was the Dragons who started brightest in the second half.
Perpignan took the most direct route to strike back within five minutes with a try for Guirado.
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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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.
At regional level the Ospreys have put their faith in Dan Biggar at fly-half and Hook will depart the Liberty Stadium in the summer to join Perpignan in his quest for more time at 10.
He does not envisage being available for the Catalans' Heineken Cup trip to Leicester a week on Saturday, but is set to make his debut against the Tigers the following weekend in the return fixture in Perpignan.
But as the Dragons grew in belief, Perpignan's summer signing Tuilagi delivered a timely boost, the giant Samoa number eight smashing through on the hour to re-establish an 11-point lead.
The Ospreys lost 17-15 in Perpignan, but earned a bonus point to help keep themselves in the running for a quarter-final place amid the tournament's now traditional complicated mathematical qualification process.
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.
Sweeney's conversion reduced the deficit to four points as the Welsh region threatened a remarkable comeback, with Perpignan short of confidence following a losing start to the French Championship campaign.
Bosc again made no mistake with the boot in front of just under 10, 000 spectators at the Stade Gilbert Brutus in Perpignan.
But moving Hook to fly-half for his 49th cap is the biggest call for Gatland as the versatile 25-year-old, who will play for Perpignan next season, is in for the dependable 96-times capped Jones.
Ulster would face Perpignan or Toulon in the semi-finals if they were to beat Northampton.
Pool One looks the weakest of the groups with London Irish, Perpignan and Newport-Gwent Dragons, none of whom finished higher than fifth in their leagues last season, grouped with Italian side Treviso.
And Devereux hopes that Hook, who has indicated he wants to play outside-half for Perpignan, is not the first of a clutch of Wales stars who may be attracted to play in France.
Wherever Gatland does choose Hook, Devereux insists him leaving the Ospreys for a three-year deal at Perpignan is a ''big loss'' for Wales especially if there are internationals outside the International Rugby Board window.
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.
Moreno moves to Leeds with a wealth of experience behind him, having made 45 appearances for Leicester Tigers across three seasons, as well as spells at San Fernando in Buenos Aires, Worcester Warriors, Brive and Perpignan, where he reached the French Championship final in 2004.
Geraghty should have put the hosts 3-0 up a minute later when he was hauled down 10m short of Perpignan's tryline by a high tackle by Rimas Alvarez, but he completely miscued the subsequent penalty kick from 30m.
Jones lifted the pressure with his fifth penalty but Scarlets replacement Jonny Fa'amatuainu was sin-binned in the 68th minute for a shoulder charge to give Perpignan further encouragement.
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