Motherwell v Celtic.
If you'd said in July that third placed Celtic would need a November win to move ahead of second placed Motherwell on goal difference we probably wouldn't have believed you.
But such seismic events often only need the collision of one or two factors. In this case Motherwell have been consistently impressive and Celtic have been consistently incompetent.
By my reckoning Motherwell have used 17 players in the SPL this season. Six of them have played every minute of every game.
If it ain't broke, don't fix it.
Celtic have used 25. Only one player has played every game.
Injuries, loss of form, tinkering, suspensions. Difficult to build momentum amid such upheaval. A dose of bad luck and a measure of bad judgement. Neil Lennon sees the problems but struggles to find solutions. That inevitably leads to questions about him and his coaching team.
Celtic could lose today and still - under Lennon or an as yet unidentified saviour - finish second. At a push - helped perhaps by shenanigans of a financial bent - they could lose today and win the title.
Life would be far easier for all at Celtic Park if those theories weren't put to the test.
Can they overcome McCall's miracle and assert their normal authority?
Maybe. Maybe not.
They were impressive in blitzing Hibs in the second half of their league cup clash at Easter Road.
But they were woeful in that first half in Edinburgh and hardly better over 90 minutes against Hibs in Glasgow.
They again overcame an early setback to dispatch Rennes in the Europa League on Thursday.
But these slow starts are unbecoming in a team of Celtic's ambition. They point to a side at odds with itself, uncomfortable in recognising what is expected of them.
And now I've fallen into the miserable trap of focusing on the Old Firm team and ignoring the achievement of Motherwell.
Motherwell aren't supposed to have played a third of their season and be in second place.
It's not how it works. So offensive is it to the normal way of things that we disregard their efforts and look instead at the failures of others.
That's the SPL way.
Consistency of selection, tight unit, good football and the confidence that comes from winning.
Spirit enough to snatch a win from 2-1 down inside the last 15 minutes to win away at Inverness last week.
Spirit enough to take 13 points from 15 since a 4-0 defeat to Celtic, a 3-0 loss to St Johnstone and league cup exit to Hibs suggested the wheels had come off.
They got their revenge against Hibs in one of the most one-sided 1-0 victories you will ever see. A performance of such dominance it suggested that, if nothing else, McCall has built a side well capable of rising above the flotsam and jetsam of the SPL.
And now a win today would open a six point gap between second and third that even Celtic's game in hand won't be able to bridge.
Champion's League chat at Fir Park is wildly premature. But it's fun. And they'll want the fun to continue for as long as possible.
Today gives Motherwell a chance to sustain the dream.
It says much about the fluctuating fortunes of these two sides that I'm finding this one impossible to call today.
How much is one Sir Alex Ferguson worth? Part Two
The eight SPL teams in action yesterday have got through 81 managers between them since Alex Ferguson arrived at Manchester United.
How many will Motherwell and Celtic add to the total?
Now: Stuart McCall
Then: Tommy McLean
In between: Alex McLeish, Harri Kampman, Billy Davies, Eric Black, Terry Butcher, Maurice Malpas, Mark McGhee, Jim Gannon, Craig Brown
Now: Neil Lennon
Then: David Hay
In between: Billy McNeil, Liam Brady, Lou Macari, Tommy Burns, Wim Jansen, Josef Venglos, John Barnes, Kenny Dalglish, Martin O'Neill, Gordon Strachan, Tony Mowbray
So, from the five SPL games played across Saturday and Sunday, the mathematical evidence tells us that:
One Sir Alex Ferguson equals 105 Scottish club managers.
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