It is unlikely that there are two men who will have a greater say in the outcome of today's Six Nations title-decider between Wales and England at the Millennium Stadium than Shaun Edwards and Andy Farrell.
The defence coaches have shaped each team this season with such overwhelming conviction that today's clash in Cardiff will resemble more the outflanking trench warfare of the First World War than a blood-and-thunder Test match.
The career curve of two former players has followed virtually the same arc from their Rugby League days, but spice to today's fixture is added by Farrell beating Edwards to the role of defence coach to the British & Irish Lions.
Wales have not conceded a try in their three victories over Scotland, Italy and France under Edwards's notable blitz defence.
It is a stark turnaround from when his team trailed by 20 points midway through their opening fixture against Ireland last month.
They rallied that day to lose by eight points, have kept up the momentum and have a chance of defending their title for the first time in 34 years.
And as far as Edwards is concerned, his side's greater experience in big matches could be the crucial aspect that decides the 80-minute showdown.
There has been a history of big games in Cardiff recently, where his side won three grand slams in the past eight years.
"Most of our team has played in a grand slam game, some in two or three, and also a World Cup semi-final," Edwards said.
"In the autumn, we were battered by injuries, we were absolutely annihilated by injury in the games, and even before that series started. We now have our best team back and hey, presto."
A Welsh win will deny England their first Grand Slam success in a decade, but stretch that victory to eight points or more and the trophy will remain in Cardiff.
Wales can win by seven if England do not out-score them by three tries, but such is the nature of England's malfunctioning attacking machine that Wales go into the match with confidence high.
England's defeat of Scotland in their opening game included four tries, but since then, only Manu Tuilagi's fortuitous touchdown against France has troubled the scorer.
In contrast, England defended a 25-phase attack in the second half against Italy on Sunday that lasted over three minutes.
It was a passage of play that was twice as long as any other in the tournament.
Farrell's high-pressure defensive ring of steel is similar to the one constructed by Edwards.
It is hardly surprising.
Farrell has been mentored by Edwards since he was 16 when they were both at Wigan Warriors, the Rugby League side.
Edwards was clearly hurt when Warren Gatland chose Farrell over him for the jamboree down under this summer, but with a friendship that stretches back over 20 years, today's match is only a rivalry, not an enmity. "I asked him for advice as a kid," Farrell said.
"He was one of the leaders within the great Wigan side who took me under their wing.
"Shaun used to put me in his car and took me to see his agent. He used to say: 'I'll look after you and show you my agent if you promise me you'll be my captain when I'm a coach'.
"He would have been 24 or 25 at that time and already knew he wanted to be a coach. He saw me as a young kid who he wanted a relationship with. I suppose that's how it is when you're from a small town.
"I don't see it as me and Shaun, head to head. It's the players who are head to head.
"When it comes to occasions like this, we'll have a beer afterwards, but beforehand we're both as professional as each other."
If Farrell can help mastermind the downfall of Wales today, the pupil will have finally outgrown the master.
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