Scotland will host Wales in a virtual knockout contest at Murrayfield on Saturday.
Lose and the Six Nations is over. Win and a final-weekend nail-biter awaits.
It was almost unthinkable they could still be battling for the championship after they suffered chastening opening-weekend defeats, but it is testament to the character of both that they have bounced back so impressively.
Scotland were limp against England but have since registered their first consecutive Six Nations wins in 12 years. Victory on the weekend would be their first hat-trick in the Six Nations era.
Wales' title defence immediately hit rocky ground against Ireland but a tenacious win in Paris was followed by another heartening success over Italy to revive hope of a final-weekend decider against England.
Scotland will have something to say about that, however, with their interim coach Scott Johnson's intimate knowledge of the visitors a sub-plot to one of the most eagerly-anticipated clashes between these countries in recent memory.
Scotland strengths/Wales weaknesses
Johnson has inspired this Scottish team to shed their one-dimensional sluggishness and play a more expansive - albeit within limitations - style of rugby.
The key has been to play to their strengths. Scotland are never likely to replicate the backline fluidity of the All Blacks, but since his arrival Johnson has drummed into his side the importance of getting the basics right.
A forgettable forward display against England aside; that has formed the bedrock of wins over Italy and Ireland.
The Irish success was backs-to-the-wall stuff but it underlined the belief Johnson has engineered in this side in such a short time.
He is aided by match-winners in the backline while the power of the back-row - led by Lions hopeful Johnnie Beattie at eight - has arguably prompted Wales to recall Sam Warburton at seven.
Ryan Jones, who retains the Wales captaincy, and Toby Faletau are a pretty handy back-row themselves but in the cauldron of Murrayfield, and with Scotland brimming with confidence, they will be on high alert.
Wales strengths/Scotland weaknesses
Wales have hardly hit the heights in defence of their Grand Slam title so far but that they remain in championship contention owes to their iron will.
A rare win in Paris a month ago was based more on desire than class before the forwards flexed their muscle against the Azzurri.
The Welsh front five are, of course, well known to Johnson after he assembled them while at the Ospreys. Whether his inside knowledge will help is yet to be seen after the barnstorming performance in Italy. Certainly at least Richard Hibbard will have a point to prove after Johnson labelled him fat during their time together in south Wales. Hibbard has since suggested that was the turning point in his career, as he shed the pounds to reclaim a Wales place and, possibly, a seat on the Lions tour to Australia.
In a match that looks too close to call it is likely the small margins will decide matters. Rain is forecast for Edinburgh which is likely to reduce the scoring and shift the focus onto the kickers. While Wales will have the trusty boot of Leigh Halfpenny to call upon Greig Laidlaw will do the job for the hosts. It is the territorial kicking battle that could be just as important, however, with Johnson handing fly-half Duncan Weir his starting debut ahead of Ruaridh Jackson. It's a gamble, but Johnson has got few of them wrong so far.
On paper this is one of the most closely-matched games in this year's Six Nations. Johnson knows the visitors inside out and has stated his inclusion of Weir - who provided drive in attack and whole-hearted defence after coming on against Ireland - is to combat their threat. It's a roll of the dice that could prove the difference.
Scotland 16 Wales 18
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