In one way Test cricket shares an imperative with the square ring of boxing. When an opponent is in trouble he needs to be finished off, otherwise he might start thinking not only of reprieve but maybe even full scale resurrection.
Certainly that was the obligation of England here yesterday when they had Australia, if not with their backs entirely to the ropes, some way from the centre of the canvas.
The trouble was that England's champion Andrew Flintoff may well have used almost all of his knockout potential, at least with the ball he used so devastatingly at Lord's two weeks ago.
Then Flintoff was a man who might, as far the Aussies were concerned, have been riding one of the four horses of the Apocolypse.
Yesterday, though, on the ground where he riveted the crowd four years ago in one of the most unforgettable of all Ashes Tests, and on Sunday wielded his bat as though it was a broadsword, there was disturbing evidence that with the fourth Test at Headingley just three days away Flintoff might not be far from the point of physical breakdown.
Unaccountably, given the strain that was showing on him when he raced to his glorious 74 on Sunday, Flintoff opened the bowling with one of the two scourges of the Australians in the first innings, Graham Onions. The other one, Jimmy Anderson, was among the mystified as Flintoff bowled seven overs at a cost of 17.
That wasn't expensive in terms of runs but it was in time and pressure because Flintoff, sadly, could not begin to reproduce the menace he had unfurled at Lord's.
Eventually, Flintoff gave way to Anderson, who immediately had the obdurate opener Shane Watson caught behind by Matt Prior. It seemed that England captain Andrew Strauss had been indulging in the aura game he now believes has gone from the Aussie armoury.
The painful truth was that the gamble could hardly have been harder on one of the few survivors of the Ashes of 2005 who has suggested he might be able to reproduce some of that old glory.
In a second spell he fell to the ground in mid-delivery, a grimace playing across his face as he tested his injury prone left ankle. A little later an on-drive by Clarke left him stumbling for the ball, then falling over again.
It was not what the big last-day crowd had come to see. What they wanted was another reminder of the frenzy that gripped the place when England scored their series-turning two-run victory, when the then England captain Michael Vaughan said, “After losing at Lord's it would have been all over for us today if we had lost. There would have been no coming back.”
Defeat for Australia yesterday would surely have brought a similar conviction in their dressing room.
However, there was never a great possibility of that once Clarke had found the rhythm which brought such an elegant century at Lord's.
The truth is that however absorbing this series becomes, if the drama stretches through Headingley to the final Test at the Oval, it is not likely to hit the levels achieved in 2005.
Then we had two beautifully matched, and motivated teams, going from ground to ground without moving too far from the position of toe to toe.
What we have in 2009 are some of the worthier aspects of Test cricket: tough and, in the performance of Clarke yesterday, Flintoff on Sunday and the swing bowling of Anderson and Onions earlier, some brilliant effort.
We are not getting, and it is probably beyond the reach of either squad, is the sense of two talented teams going to their very limits.
For England yesterday the challenge could not have been more concentrated around one vital need. It was to take the third Test and put Australia on the very edge of series defeat.
There were several reason why it didn't happen, why Australia in the end moved so easily away from a potentially devastating slide to 2-0 after starting the day 25 runs behind with two wickets down and captain Ricky Ponting brooding darkly in the dressing room.
One was that if the Australians have indeed lost much of their aura, along with more than half of arguably the greatest team in cricket history, they do retain some quite important qualities, including a fighting instinct proofed against even the most unpromising circumstances and some quality of the highest class.
Is Clarke great? Is he rescuing at least a little aura for an Australian team substantially outplayed until the last day here?
The debate will no doubt linger beyond the course of this series. Certainly it is true he didn't exactly storm the highest ground of confidence after reaching the 80-run mark in his 12th Test century.
On one occasion a ball from Stuart Broad appeared to feather itself against a Clarke stump without disrupting the bail and on another the Australian vice-captain was caught in the slips by Anderson — but only after a no-ball had been signalled.
By this hazardous stage Clarke had already done the essential business, which is say guide Australia towards the fourth Test still within touching distance of their challengers.
This was the day England were supposed to take control. Instead, they could only mourn the coup-de-grace that didn't happen.
And, perhaps most vital of all, wonder quite what Freddie Flintoff has left.