Alastair Cook could top list of all-time Test run scorers, says Rob Key

Sky Sports Cricket's Rob Key looks back at Alastair Cook's record-breaking fifth Test double hundred, and says the England opener has a chance of toppling Sachin Tendulkar on the list of all-time Test run scorers...

Cook is a guy who is forever underestimated and forever proving people wrong. Well, he's done it again at the MCG with an absolutely extraordinary innings.

He's an extraordinary cricketer with an extraordinary record. When you look at who he's gone past and where he now is on the list of the all-time leading Test run scorers, there's no other way of describing him other than extraordinary.

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There's no point in comparing him with the Brian Lara's of this world, but Cook's position on that list should never be underestimated because of the fact he's done it as an opener.

He's constantly been at the coalface if you like. He's had to do it time and time again against the new ball. He's always had to face the best bowlers when they are at their freshest. He's also had his tough times, when it seems like his technique has deserted him but never once has he relented, never has he given up and thrown in the towel. He's just kept pushing on and finding a way of getting past all the self-doubt that comes with bad form and he's gone on to overcome adversity every single time.

As a cricketer, every player wants to be known as a great but if you can be known as a mentally tough player as well, scoring your runs at the tough times when everything is going against you, that's something Cook is probably most proud of.

I never had any doubts about him rediscovering his form as long he wanted to continue playing and he never felt like he was coming to the end of his career. All the talk was that he was putting in the hours and practising hard to sort his game out. With that being the case he was always going to come good.

He played very well. It was a really important partnership for England. He gets a lot of stick for his batting but the batsmen are there to score runs and he’s there to take wickets. Runs from him are a bonus and it doesn’t really matter how he gets them.

People forget how young he is because he's been around so long. It's not like he's 38 or 39, he's still got a few years left in the tank yet if his body allows it. And on the evidence of the last couple of days there's nothing wrong with his body. You always feel with mentally tough players like Cook and Steve Waugh, if they want to continue playing and still have the hunger for it, they will always come good.

All the questions about whether Cook still had the hunger have now gone because when you get a hundred some players can relax, but to go on and make it count like Cook has done shows a player still as hungry as he ever was to score big runs. There's been a lot of players over the years that might have gone through the gears a bit after reaching a hundred, playing a few shots, taking a few more risks but Cook doesn't. He just continues on his same way because a hundred is not enough for him.

He said that there's always been a lot of moving parts to his technique and when you have a lot of moving parts, you need them all to be in sync at the same time.

His game hasn't really changed too much throughout his career. There was one point where he changed his trigger movements as a batsman during the Pakistan series at home in 2010. He struggled a bit and went back to his old way, and what followed was the Ashes series Down Under during which he had an unbelievable time of it. Again he was under pressure going into that series but he turned things around, scoring 766 runs at an average of over 127.

I’d bat a bit longer in the morning to try and get as many as possible. I’d also bat just to annoy the Australian openers. It would certainly annoy me having to field again because all I’d want to do is warm up have a hit and stick my pads on.

I remember watching when we first saw him on Sky Sports as an England U19 captain at the youth World Cup and I don't think he's changed too much since then.

His technique has often been pulled apart but it is what it is. Whether you play against him or with him, he's always had a lot of movement, he's always gone back and across and he's stuck to what he knows. He's always played those punched drives, he's always clipped the ball off his hip but his real talent, which is up there with any of the great players, is the way he pulls and cuts. That's his rare gift along with his mental toughness.

But for everything he achieved in the game he's a very humble man. He said himself that he almost feels sorry for Lara after going past him. You look at Lara with that big back lift, his attacking game and the way he used to take the bowlers down in awe, but Cook has proved there are other ways to do it.

And as I mentioned earlier, out of all those players on the all-time Test run scorer list - the players he's gone ahead of and the players he's chasing down - Cook is the only one that has done it as an opener. He batted at number three for England during a home summer early on his career, but for the rest of his career, whether it's at the start of the day's play or for five overs at the end after a long day in the field, he's always gone out to face the music. Everything he's done, he's done as an opener which I would say is doubly difficult.

Mo’s had a really tough tour and he’s got to the point where a decision has to be made to stick or twist. Does he block his way out of trouble or hit his way out of trouble? He went with trying to hit his way out of bad form but it didn’t really come off.

How far could he go up the all-time Test runscorer list?

It's scary to think really because he could chase them all down. It just depends on how his body holds up because it looks like he's no less hungry for runs than he ever was.

The problem is, and it happens to all sportsmen as they get older, when you are young and out of nick you don't start thinking about your eyes, your head or whether you've still got it. The older you get the more you start thinking about those sorts of things, whether your reactions have gone and whether you're still the player you always were.

After his latest performance, Cook has shown it was just another little blip and he's still got plenty left in him. He's only 33 and he could play for another five or six years. If he does that, who knows? He could get right to the very top!