Biarritz produced an epic display of power rugby to beat the Dragons 49-13 in France on Sunday and put a foot in the quarter-finals of the Heineken Cup.
The French side, beaten finalists three years ago, opened up a nine-point gap as Pool Two leaders ahead of next Friday's return fixture in Newport.
Biarritz battered the Dragons into submission up front, and they claimed a bonus-point try just after half-time when England back Iain Balshaw touched down for the first of his double.
Wing Takudzwa Ngwenya, scrum-half Dimitri Yachvili and substitute Valentin Courrent also crossed, while there was a penalty try and seven successful kicks from Yachvili, who finished with 22 points, before Courrent slotted the final conversion.
The shell-shocked Dragons had to content themselves with a consolation score by centre Tom Riley, while fly-half James Arlidge kicked the conversion and two penalties.
It was the Dragons' heaviest Heineken Cup defeat since they crashed 37-0 to Stade Francais in 2003.
And they face a considerable psychological challenge to turn things around in time for the rematch, even though Biarritz have sometimes struggled on the road in Europe.
Balshaw and his fellow England international Magnus Lund featured in a Biarritz team that knew it would take charge of Pool Two by extinguishing the Dragons' threat.
And the Dragons arrived at Parc des Sports Aguilera without their towering Wales lock Luke Charteris, who was nursing a thigh injury, so Robert Sidoli deputised in the second row.
The Dragons, beaten on all five of their previous Heineken Cup trips to France, fell behind to an early Yachvili penalty and then lost their Wales flanker Dan Lydiate through injury.
New Zealander Haoni MacDonald replaced Lydiate, whose afternoon lasted barely six minutes, as Arlidge slotted an equalising penalty.
Biarritz dominated territory, but the Dragons hardly helped themselves when Hugh Gustafson was sin-binned for a professional foul before his fellow prop Peter Bracken committed a high tackle and Yachvili booted the resulting penalty.
The Dragons encountered a torrid time in the scrums, where France prop Fabien Barcella proved particularly destructive, and the visitors conceded an 18th-minute penalty try that Yachvili converted.
But matters soon deteriorated further for the Dragons, who saw number eight Grant Webb yellow-carded and then conceded two tries during a damaging three-minute spell.
Lund created the first, catching the restart following an Arlidge penalty and sending Yachvili over, before Ngwenya intercepted an ambitious midfield pass and sprinted 40 metres unopposed.
Yachvili slotted both conversions, giving Biarritz an unassailable 30-6 advantage as half-time approached.
It was already a case of damage-limitation for the Welsh team, but they were powerless to prevent Biarritz from claiming a bonus-point try just five minutes after the break.
Balshaw was the beneficiary of more mighty work by the Biarritz pack, touching down wide out with an overworked Dragons defence once again shredded.
Dragons coach Paul Turner began making changes from the bench, but it had little impact as a sharp Yachvili break and well-placed kick enabled Balshaw to claim his second try.
The Dragons, to their credit, kept plugging away despite the gulf in class, and Riley's touchdown at least gave their small band of travelling supporters something to shout about.
Biarritz though, had long since sealed the deal, and they know a quickfire winning double over the Dragons would effectively wrap up the group and secure a quarter-final place.
Tries: Penalty try, Yachvili, Ngwenya, Balshaw 2, Courrent
Cons: Yachvili 4, Courrent
Pens: Yachvili 3
For the Dragons:
Pens: Arlidge 2
Biarritz: 15 Iain Balshaw, 14 Ilikena Bolakoro, 13 Karmichael Hunt, 12 Damien Traille, 11 Takudzwa Ngwenya, 10 Julien Peyrelongue, 9 Dimitri Yachvili, 8 Florian Faure, 7 Samiu Vahafolau, 6 Magnus Lund, 5 Jerome Thion (capt), 4 Pelu Taele, 3 Remy Hugues, 2 Benoit August, 1 Fabien Barcella.
Replacements: 16 Romain Terrain, 17 Eduard Coetzee, 18 Manuel Carizza, 19 Trevor Hall, 20 Valentin Courrent, 21 Arnaud Mignardi, 22 Nicolas Brusque, 23 Campbell Johnstone.
Dragons: 15 Jason Tovey, 14 Aled Brew, 13 Rhodri Gomer-Davies, 12 Tom Riley, 11 Richard Fussell, 10 James Arlidge, 9 Wayne Evans, 8 Grant Webb, 7 Gavin Thomas (c), 6 Dan Lydiate, 5 Rob Sidoli, 4 Adam Jones, 3 Peter Bracken, 2 Duane Goodfield, 1 Hugh Gustafson.
Replacements: 16 Tom Willis, 17 Ali McKenzie, 18 Gethin Robinson, 19 Hoani MacDonald, 20 Joe Bearman, 21 Alex Walker, 22 Martyn Thomas, 23 Matthew Watkins.
Referee: Andrew Small (England)
Assistant referees: Rob Debney (England), Paul Dix (England)
Assessor: Brian Campsall (England), John Sheehan (Ireland)