Leinster will have to take a wait-and-see approach as to where they will be for the Heineken Cup quarter-final after overcoming the Ospreys 36-3 with five tries at a raucous RDS last night.
The Welsh came with nothing to gain or lose and that made them an extremely dangerous proposition given their fearless attitude at a ground where they have won two PRO12 League Grand Finals.
Leinster coach Matt O'Connor had pointed to a swift start as a necessity. It took them just shy of three minutes to leave their own half, Rob Kearney's grubber taking them there.
Out-half Jimmy Gopperth sparked Leinster's final try against Castres with an unlikely turnover. He showed this wasn't a one-off by picking another pocket for a gain of ground.
The signs of intent began to pop up, Cian Healy charging around the back of a lineout, Eoin Reddan accessing fast ball and delivering real tempo for his outside backs.
Healy turned on the power at the scrum to drop Adam Jones to his knees, Gopperth striking from short range for 3-0 in the ninth minute.
This was quickly undone when Dan Biggar struck a penalty from 46 metres, Justin Tipuric forcing Shane Jennings to hold on too long on the floor.
Replacement Matthew Morgan's – he came on for big Ben John – beautiful pass put Aisea Natoga into space and Leinster onto the backfoot but Rob Kearney came to the rescue at the breakdown.
Northampton put forward the template for rebounding from a hometown defeat by Leinster and it was based on physical brutality.
Second row Ian Evans took this a step too far, literally, maiming Mike McCarthy with what Video Official Laurent Valin judged to be foul use of the boot.
Once identified, referee Romain Poite had no option but to red-card Evans, making scrum time a liability for the Ospreys. It took Leinster time to make the extra man count.
When they did, it came from a lineout-maul that travelled a full 20 metres before being blatantly and illegally sacked for a penalty try, converted by Gopperth in the 33rd minute.
Then, Martin Moore didn't freeze when he got into space, delaying his shovelled ball to Gopperth, who was miraculously prevented from providing number two by the feet of Jeff Hassler
It was a temporary hindrance. Dave Kearney, Jamie Heaslip and Healy were prominent in bringing play to within sniffing distance, Healy on hand to close the deal. Gopperth's conversion made it 17-3 at the interval.
The stage was set for the Ospreys to fall away and for Leinster to move menacingly into bonus-point range. But, the game deteriorated as the home side looked for tempo at the expense of composure.
Zane Kirchner, on for Rob Kearney, made an instant impact, his drive for the corner almost turned into a try by Dave Kearney.
The pace was there, the patience and precision not so much. A wayward clearance by Brian O'Driscoll handed the ball back to the Ospreys, the centre making amends with a textbook poach.
All the while, the minutes were moving on, the quarters too. Gopperth finally put Leinster into the right area from a superb touch-finder.
The maul was taken down and the scrum prompted a power surge, taking Heaslip to the line where Poite signaled a penalty try for interference by Rhys Webb. Gopperth added two for 24-3 just past the hour.
Leinster were three-quarters of the way towards five points. They put a choke-hold on an Osprey counter. Heaslip tore away from the rear of the scrum. Reddan fumbled the ball forward.
Tension and frustration was building. The crowd was lifted by the entrance of Richardt Strauss. They owned the ball and the fourth try duly arrived from Jordi Murphy's hard line in the 73rd minute.
From there, it was mile-a-second stuff as Isaac Boss's support line took him to glory for the fifth and Heaslip was inches away from a sixth.