Former England captain Michael Vaughan has declared Steve Smith will be the key to unlocking a Test series victory for Australia over India in the Border-Gavaskar Trophy.

It’s a factor not many would recognise, which Vaughan believes is Smith’s killer asset.

His eyes.

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“Steve Smith back at number four, those two innings that we saw in the one-day series, he seemed to have had that flow (back),” Vaughan said on Tuesday.

“We’ve seen Steve’s eyes when he’s playing well, he just looks completely composed, calm out in the middle. He found that.”

But a confident Smith doesn’t mean Indian veteran Virat Kohli will just disappear.

“I think Virat Kohli, when he comes here, when he lands in Australia, he lands and knows that this is a place that he’s had a huge amount of success,” Vaughan said.

When it comes down to it, it’s the roles of Smith and Kohli, both batting at number four for their countries, that Vaughan believes will ultimately decide who wins.

“You could argue which of the number fours has the biggest series could be the deciding factor of the whole series,” he said.

“In the last four or five years, without question, these two teams have been the best two teams (with their) skill set (and) mentality.”

But Vaughan may have the equation for India to overcome Australia.

“I’m a big believer when you play Australia, there’s only one way to play them. That’s being on the front foot, being aggressive and trying to ruffle a few feathers,” he said.

“Can Rohit (Sharma) arrive and kind of captain in a similar sense (to Kohli)? I think that’s going to be the big challenge for India over the course of the next few weeks.”