It may well go down as the moment Australia truly believed they were set to win the Ashes on English soil for the first time in 18 years. At the very least, Pat Cummins' top-of-off-stump pearler to defeat England's captain Joe Root first ball has set down a definitive blueprint for what the Australians will be attempting on day five at Old Trafford, according to no less an authority on batting than their talismanic run maker Steven Smith.

There was a period on day four when England looked capable of elbowing their way back into the contest, as Stuart Broad and Jofra Archer delivered two of the most compelling spells of a series dominated by the bowlers on both sides. However Smith emerged as Australia's' bulwark yet again, cuffing 82 with help from Matthew Wade and Tim Paine to grant the visitors a handsome lead and the chance to bowl in murky light during the final half an hour.

Cummins responded by drawing an error from Rory Burns in the first over, and followed up with a ball that could not have been bettered to flick Root's off stump. He had copped a similar delivery from Ryan Harris at Durham in 2013, but this one will be remembered not only for the quality of the ball but the importance of the moment. Smith said that it made crystal clear what the Australians needed to do on the final day.

"I think it will be difficult, particularly while the ball is hard. I found when I first went out to the middle, when you bowl a good length, there was enough up and down and sideways movement. My first 20 or 30 balls, I felt pretty vulnerable when they were bowling that good length," Smith said. "Patty hit it beautifully tonight, I think that ball to Root is a blueprint of what we need to do tomorrow, first thing in the morning, and the quicks to keep hitting that top-of-the-stump length and let the pitch do its thing.

"Mixed in with a good bouncer to play with their feet, and maybe get a bit of up and down as well. It's the length we've been trying to hit on Root, particularly early in the innings. It's worked a few times. He's got out first ball a couple of times and early on a few time with a very similar ball. That's the sort of length we tried to hit. Fortunately Patty did it first ball. I have no idea if it moved, kept low or what but I think it's the length that's the most important thing. That was a good length."

Bowlers on both sides have been able to dictate terms with seam more so than swing, and Smith believed this was deliberate: a scrambled seam delivery that can move either way off the pitch being far harder to adjust for than something that moves through the air, though as Mitchell Starc demonstrated to Johnny Bairstow, it can make for a devastating variation if conditions are right. At the same time, David Warner's struggles have been unprecedented in his career, leaving him asking Smith, among others, for answers.

"I think it's off the pitch, that's the key to try and hit that," Smith said. "I don't know what it does when they scramble it, but I guess it just hits the ball in a different spot then can move sideways, there is no doubt in my mind that the seaming ball is the hardest thing to play in the game. You don't have time to react so you have to play the line and if it goes in, you are a chance of hitting the stumps and getting lbw, and if it goes away you are a chance of nicking it.

"A couple of our guys have exploited that pretty well on this wicket and if they do that again and hit the top of the stumps, that same length as the Root ball, hopefully we can see a lot of bowled, lbws and caught behind the wickets. It's been tough on the new ball for both sides. The ball's probably done its most when it's new. When it gets a little bit softer it doesn't do quite as much, it gets a little bit easier. They've bowled pretty well with the new ball. They're both particularly good bowlers to left-handed batters, both Broad and Archer. It's not been easy for Davey and Marcus but they're trying their hardest.

"We've talked, a few different things here and there. Just trying to form a plan to get through Broad. He's admitted himself that Broad's had the wood on him throughout this series and he's been talking to myself and Justin and Hicky, I think, about ways he can play. He's tried a couple different ways and they haven't quite worked. but Davey's a quality player and he hasn't had a great deal of luck this series either, hopefully he can turn it around and get a big one for us at The Oval."

As for his own incredibly prolific series with so much chaos around him, Smith said he had wanted to be involved when the games were at their most difficult, using his singular skills to turn numerous scenarios back around to Australia's' favour. "I think when it is tough you want your experienced players to step up," he said. "I've played quite a lot of cricket now. I like to get into those situations and try and be the one to take the team through.

"I was able to form a really good partnership with Matty Wade, who I thought played really well today as well. That partnership was really handy for us at that stage. England were really up and about with us four down but a good half an hour of batting and things got a bit easier for us and we were able to form a nice partnership, and hopefully one that will set us up for this game.

"I'm not in the game for personal accolades, I'm here to do my job and score as many runs for the team as I can and fortunately this series I've been able to score quite a few and help the team as much as I can. Hopefully I can do that again next game."