Cullen knows every point counts
Champions Cup: Northampton v Leinster (live KO7.45, BTSport 2)
Leinster will look to spook Northampton with speed of movement rather than lean too heavily on their strength for the fight.
That is the immediate impression from coach Leo Cullen's decision to hand Adam Byrne his European debut, promote Hayden Triggs ahead of Mike McCarthy in the engine room and look to Rhys Ruddock as their back-up plan on the bench.
There is no room for Zane Kirchner, McCarthy or Dan Leavy in the 23-man squad as Jack Conan's form has proved too good to ignore.
Former Leicester Tiger Cullen is all too aware of what awaits at Franklin's Gardens in the East-Midlands.
The December 2013 blitz of Northampton was undoubtedly the best performance of Matt O'Connor's ill-fated tenure, one they could never repeat.
It was founded on a lightening start conducted at bullet-fired speed.
"Teams gain confidence or lose confidence by how they sometimes start," said Cullen.
"We know they're going to be emotionally fired up for this game.
"You just look at the pool and how close it is. There's very fine margins.
"We're just about sitting on top on six points, the team which is sitting on the bottom is on four points, so it's incredibly tight."
It could all be changed utterly by close of play later this evening.
"We've tried to prepare as best as we possibly can," claimed Cullen.
"We have been constrained by guys coming back in and it's been a short week with a Friday game coming off the back of a late kick-off on Saturday against Dragons.
"It's accelerated learning."
Leinster will have to be au fait with the details of the game and the impact of the result for the return leg at The Aviva next Saturday.
"Literally, every little thing matters, every point does count and we have to make sure we realise.
"We're going out to win the game, clearly, but when you're in the situation you need to make sure you can get what you can out of it."
Leinster have been reminded of the precarious nature of this competition by none other than Northampton.
"You've seen some of the turnarounds in these games over the years; it's incredible.
"Even this fixture, three years ago when we put 40 points on Northampton over there and then to lose the following week and just the knock-on effect that had.
"We had a bonus-point toward the end and Jamie Elliott got that breakaway try to deny us a bonus point.
"It meant, all of a sudden, we had to play away in a quarter-final against Toulon, which happened to be my last game of European rugby I'm afraid," smiled Cullen.
Seán O'Brien will be able to blend into a back row with his long-time companion Jamie Heaslip and new sensation Josh van der Flier.
"He's been unbelievably consistent; some huge performances, not just this season, but at the end of last season too," said O'Brien his fellow flanker.
"He's been keeping the heat on the whole lot of us I think. He's a great professional as well and someone who is only going to get better too.
"He just does his job, he doesn't make any mistakes, he knows his detail and his work-rate is incredible," he vouched.
"He's a big part of this team now."
Northampton: B Foden; K Pisi, L Burrell, JJ Hanrahan, J Elliott; S Myler, N Groom; A Waller, M Haywood, P Hill, M Paterson, C Lawes, J Gibson, T Wood (capt), L Picamoles.
Leinster: R Kearney; A Byrne, G Ringrose, R Henshaw, I Nacewa (capt); J Carbery, L McGrath; J McGrath, S Cronin, T Furlong, D Toner, H Triggs, S O'Brien, J van der Flier, J Heaslip.