January 3, 2017. It is close to half-past noon at the Sydney Cricket Ground when David Warner manoeuvres Wahab Riaz through backward point, runs three, and leaps, fist pumping the air. He has become only the fifth batsman to score a hundred before lunch on the first morning of a Test match.

At that point Warner is batting on 100 off 78 balls, and he has hit 17 fours. At the other end, Matt Renshaw, having faced two more balls than his opening partner, has made 21 with two fours.

Warner falls in the sixth over after lunch, for 113 off 95 balls. Renshaw bats on until the sixth over of the second morning, when he is dismissed for 184 off 293 balls.

Warner, 30, and Renshaw, 20, both bat left-handed and throw right-handed, but the paths they took to the Australian Test team couldn't have been more different. Warner made his T20 debut for Australia before he had even played first-class cricket. Renshaw had only played 14 first-class matches before making his Test debut, but was - and is - yet to play T20 at any level, international or domestic.

At first glance, Renshaw should be the anomaly and Warner the prototype of the Test-match opening batsman in the T20-dominated cricketing landscape they inhabit. This, however, is not so. A majority of the world's Test line-ups now begin with a pair of opening batsmen who are not part of their country's first-choice T20 side. Alastair Cook and Haseeb Hameed. Tom Latham and Jeet Raval. Kraigg Brathwaite and Leon Johnson. Stephen Cook and Dean Elgar. Dimuth Karunaratne and Kaushal Silva. Azhar Ali and Sami Aslam.

Ten of those 12 have never played T20s for their country. Neither of the other two - Alastair Cook and Latham - has played one since November 2015. Brathwaite - who has been a first-class cricketer since 2009 - and Hameed, like Renshaw, haven't even played T20s at the domestic level.

As a result of this, the way Test teams combat the new ball has changed.

Eight of the ten most prolific opening batsmen of this millennium have scored their runs at a strike rate of 50 or more. Four of them - Virender Sehwag, Warner, Chris Gayle and Matthew Hayden - have done so at 60-plus strike rates.

Sehwag, Gayle, Hayden and Tillakaratne Dilshan were thought to have changed Test cricket forever with their aggressive approach at the top of the order. That hasn't been the case.

The generation that has followed them seems to have retreated from "see ball, hit ball" to "see off new ball". Only two of the ten top run-getters among openers since the start of 2015 - Warner and Martin Guptill - have scored their runs at 50-plus strike rates.

Aakash Chopra, the former India opener, suggests teams worldwide are looking for solidity at the top of the order to try and arrest the trend of collapses that has beset Test cricket over the last few years.

"I think technique has become slightly compromised a little bit in the recent past," he says. "The number of collapses is unbelievable - if there's anything in the pitch, you'll see a collapse - whether it's spinning, it's swinging, whatever. If there is something out of the ordinary, there is an issue. So that fact perhaps explains that teams maybe realise you need openers with better skills."

Given that the skills required to open in Test cricket are so different from those required to open in T20, Chopra says a number of batsmen have realised they might be better off specialising in the format they are best suited to.

"I feel the time has come when people have realised that as a Test opener, I'm okay being a Test player, I'm okay not to play T20 cricket. And the people who are playing T20 cricket are perhaps also okay with the fact that they're only going to play T20. There will still be exceptions; KL Rahul is an exception, because I actually see him as this modern-day batsman who will fit into all three formats.

"Someone like M Vijay, I think, has made up his mind, that Test cricket is my first priority, everything else is okay. Same is the case with Tom Latham - he's again a Test batsman in the Test mould."

There is, concurrently, a parallel universe of openers who only play short-format cricket, containing the likes of Jason Roy, Johnson Charles and Aaron Finch. The few that have crossed over to Test cricket, such as Guptill and Alex Hales, have generally struggled to express themselves. England dropped Hales after he averaged 27.28, and scored at a strike rate of 43.84 in his first 11 Tests.

A group of attacking openers who made eye-catching starts to their Test careers - Adrian Barath, Phillip Hughes, Hamish Rutherford, Shikhar Dhawan - have not made a sustained impact, for one reason or another, and of their generation only Warner and Tamim Iqbal have gone on to establish themselves as regulars.

Perhaps this could be because the likes of Sehwag and Gayle came to T20 late in their careers, by which time they were already successful long-format batsmen. Their style of play happened to suit T20 as well. The generation that replaced them had to adjust to T20 before they were fully formed.

Chopra expects the next generation to be more comfortable shuttling between formats, and sees Rahul - who has scored hundreds for India in all formats - as a prototype of that new kind of opener.

"It's a process. There will still be exceptions to the rule," Chopra says. "I keep mentioning KL Rahul because he is that modern-day batsman. Sometimes we underestimate evolution, we believe that this is how it should be, but some humans have evolved so much that they say a Test opener can easily be a one-day opener or a T20 opener.

"And it doesn't even have to be a Sehwag. KL Rahul is otherwise a very correct kind of, straightforward kind of batsman."

Chopra says Vijay is similar to Rahul in the sense of having an orthodox technique as well as an ability to hit over the top, but found it more difficult to adjust between formats than Rahul - who arrived later on the scene - has done so far.

"Temperamentally, for a while, [Vijay] was shuffling between Test, one-day, T20," Chopra says. "He wasn't sure of what he wanted, and therefore he was highly uncertain, but now he's made up his mind that, okay, he's solely a Test player.

"So it'll be interesting to see. In five to seven years, you'll find another new phase coming in. You'll have batsmen coming in who are equally successful in Test cricket, equally successful in one-day cricket, and will not even have to slog in T20."