England v South Africa: Alastair Cook sets example for England - Jonathan Agnew

After being thrashed in the second Test against South Africa, England had to show something different in the third match at The Oval.

Alastair Cook, the former captain, led the way. In what was a first day of 'proper' Test cricket, he played a proper Test innings.

I was actually quite surprised by the way England reacted to that 340-run hammering at Trent Bridge. They were bang to rights but, rather than holding their hands up, they tried to counter the criticism.

The message they should have taken was a reminder that in Test cricket you cannot always play freely and expect it to work all the time. You will get bitten.

In reality, the men most likely to show how it is supposed to be done were Cook and Joe Root, with Cook the one rising to the challenge of a magnificent South Africa attack in tricky conditions.

Having said that, all of England's batsmen fought hard, with Cook's 82 not out taking them to 171-4 on a rain-hit day.

• Report: Cook defies South Africa on rain-shortened day

Early on, the opener played a fluent drive that made me think, 'he's in good touch today'. It's always a positive sign when Cook is getting forward and driving straight.

He is one of England's most prolific run-scorers, so he knows how to play, but there was also an element of giving the rest an example to follow after the feeble batting we saw in Nottingham.

Cook batted deep in his crease, possibly to counter the bounce, and left the ball well, often when he knew it was going over the top of the stumps.

Still, when South Africa got it right, they bowled brilliantly, probing as the ball both swung and moved off the pitch.

For that reason, Cook can look back on what he has achieved today with immense pride. It wasn't pretty, but it was hugely satisfying.

While Cook batted throughout the day, his opening partner, Keaton Jennings, lasted only nine deliveries before falling for what is his third duck in five Tests.

Indeed, after making a century on his debut and following that with 54 in his second match, Jennings has made scores of 8, 33, 0, 3 and 0.

Like at Trent Bridge, when he got bowled through the gate by Vernon Philander, his technique let him down.

Now, I do not know if the habit he has of planting the front foot and pushing at the ball is the way he plays all the time, or just something he is doing because he is out of form.

But I can say with certainty that, unless he changes, he will be found out at this level.

If he is not offering a huge gap between bat and pad for the ball to travel through, then he is susceptible to giving an edge, like he did on the first morning here.

In some ways, I feel sorry for him, because he is being thrust out to open the batting after only being given a diet of Division Two bowling in the County Championship - and even then he hasn't made many runs for Durham.

Remember, Haseeb Hameed, England's other success story from the winter, was left out because of his domestic form.

But that doesn't stop me fearing for Jennings, who now faces a big second innings and fourth Test at Old Trafford next week.

He is likely to be given every chance to succeed - coach Trevor Bayliss has stated in the past that he would rather give a player one game too many than one game too few. Indeed, it's my understanding that England would have retained Gary Ballance for this Test had he not broken a finger.

Ballance's replacement at number three, Tom Westley, showed signs of promise in his 25.

He reminded me of John Crawley, formerly of England, Lancashire and Hampshire, with the way he whipped the ball through mid-wicket using his bottom hand.

The right-hander stood tall, followed Cook's example to leave well and showed good judgement.

Westley may have to straighten his technique - he was slightly turned around giving the edge that led to his dismissal - but, for a first knock in difficult circumstance, it was OK.

His fellow debutant Dawid Malan got a much more brutal introduction to Test cricket, probably answering any questions that he may have had about just how hard the game is at this level.

He took 15 balls to get off the mark, which can't have happened very often when he has been playing for Middlesex, and then got bowled by a wonderful yorker from Kagiso Rabada.

It was a fantastic piece of bowling, with pace and swing leaving Malan on the turf.

If the batsman can take any crumb of comfort, it is that ball would have got pretty much everyone out.

It was deliveries like that, and those produced by Philander and Morne Morkel, which give further credit to the innings played by Cook.

He dug deep and enjoyed the challenge. That is what Test cricket is all about.

Jonathan Agnew was talking to BBC Sport's Stephan Shemilt