Kevin Pietersen's fifth Test wicket might just be the difference between England winning and drawing this match in Adelaide. It is that significant.
England's latest man-of-the-moment inflicted a massive body-blow by removing Michael Clarke just before stumps to leave Australia on 238-4, still 137 behind.
If the weather stays fair, England will relish bowling with the new ball at a brittle Marcus North and thereafter a tail that is unlikely to offer protracted resistance and, from this position, they should go 1-0 up in the series.
But had Clarke still been there at the close alongside the indomitable Mike Hussey, Australia would have faced the final day with fresh optimism.
Their positive partnership wiped 104 off the arrears and a repeat dose on day five would have changed the complexion of this game appreciably.
So Pietersen's joy at claiming Clarke's wicket was entirely understandable in the context of the Test and his own vastly-improved form.
Andrew Strauss was clearly fearful that Australia would get in front of England if they declared on their overnight total 551-4 and so batted on.
Had Clarke still been there at the close alongside the indomitable Mike Hussey, Australia would have faced the final day with fresh optimism.
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If he goes one way, Strauss does tend to err on the conservative side. For example, the bold thing to do in this Test would have been to include Monty Panesar at the expense of Paul Collingwood.
In this case his caution was well-founded. The extra runs England added before declaring on 620-5 proved necessary as they struggled to breakthrough with the new ball.
As is his way, Shane Watson looked authoritative at the crease without going on to get the hundred his side so desperately needed from him.
He's now scored 11 fifties and two hundreds in his career - a conversion rate that must improve if he is to be considered a genuine Test opener in the long-term.
Australia were always going to struggle to replace two batsmen of the quality of Matthew Hayden and Justin Langer.
They gave Chris Rogers and Phil Hughes a go before promoting Simon Katich and Watson from the middle order and while have stepped into the breach admirably, they remain manufactured openers with something to prove.
In Watson's defence, he was dismissed this time around by a fine piece of bowling from Steven Finn showed far more control in Australia's second innings.
He's an intelligent young man who is quickly coming to terms with bowling with a soft ball on Australian pitches and I hope that at some point he gets the luxury of taking the new ball because I'd love to see what he can do with it.
While the pitch remains pretty flat there is some rough there and the odd ball has turned dramatically which is where Pietersen - and more realistically Graeme Swann - should come into their own.
Swann's extra class was sufficient to account for Ricky Ponting - no bad player of spin by any means - and if he can continue to strike the right length there is just enough help in this largely lifeless surface to wrap up what would be a thoroughly-deserved victory. Weather permitting.