Kevin Pietersen: 'I like to stand up and be counted on days when it's really tough' © Getty Images
Kevin Pietersen does not lack for confidence. His only concern is when, and how much - the sort of self-belief England's middle-order desperately craves at the moment, especially when Ian Bell and Paul Collingwood fall for ducks in the space of seven balls. "I like to stand up and be counted on days when it's really tough," he said of his 12th Test hundred, and today was undoubtedly tough. It was also a lesson in rearguard batting that some of his colleagues would do well to take heed of.

Something clicked with Pietersen today. There was a welcome return of the exuberant flamingo-flick through midwicket. His cover-drive, on the up and against the swing, made an appearance once or twice. He celebrated the hundred with his star-jump and nearly even raised a smile, which has certainly been lacking in recent times. This wasn't quite the carefree Pietersen of two years ago, when he dominated Muttiah Muralitharan so brutally. In fact, it was his slowest hundred for England to date, but its worth was unquestioned.

"Losing 3 for 2 is obviously not what you plan to do straight after lunch," he said, "but that's when I like to stand up for England. I like to score runs when it counts. I'll go home tonight and feel a lot better. It's nice to score when everything's good and happy, sure. But the hundred I scored in Napier when we were 30 for 4, that was another one. The Ashes hundred [at The Oval]. There have been quite a few. I've scored when England have been in the dumps.

"I like to stand up and be counted on days when it's really tough. I think it's a good judge of character, and I came out and just wanted to enjoy myself. I came out and scored in pretty good areas, my hands were working well. [It's] all good."

If it's all good for Pietersen, it's far less so for his colleagues. As much as England desperately try to prove that everything is smelling of roses, as typified by their selection of the same side for a record five Tests in a row, this afternoon's performance - losing 3 for 2 in 13 crazy deliveries - smacked of complacency. If anything, Pietersen's ton pastes yet more paper over the cracks of their middle-order. Today, they resumed after lunch on a relatively secure 84 for 2 before Andrew Strauss flayed at a wide one from Kyle Mills. Bell soon followed, walking across a straight one from Iain O'Brien, and Collingwood edged nervously and needlessly to slip. The ball was doing all-sorts, but there was little evidence from England that they had the wherewithal to cope.

Peter Moores came to Collingwood's defence after the first two Tests, but for all his reassurance that England's middle-order possesses so many batsmen averaging in the forties, for how much longer?. Runs, runs, runs are what the pair need, though Pietersen remained aggressive in his defence of his colleagues.

"It's obviously a struggle and it's hard," he said. "I saw a list of the batsmen who are the top run-scorers in county cricket at the moment, and none of those guys are better than Ian Bell or Paul Collingwood. Not one of them can touch Bell or Collingwood.

"It's just a matter of time; the cycle of life has it that you'll have good days and bad days, and unfortunately they're missing out at the moment. Bell scored a hundred three games ago; Collingwood, yes, he's missed out. But he's an important member of our team and a great guy. It's hard when people criticise these people."

Joining Pietersen was Tim Ambrose, England's nuggety (and possibly underrated) wicketkeeper, with whom he put on 161 for the sixth wicket - the second-highest at Trent Bridge. Ambrose thwarted New Zealand at Wellington, when England were in similar dire straits at 136 for 5. Ambrose is a feather in Moores' cap - which has plenty of room for more - and his shot-laden 67 came under immense pressure. Matt Prior, who is scoring runs for fun at Hove, continues to breath heavily down his neck, but Pietersen is confident England have found themselves a wicketkeeper to stick with.

"It's nice batting with Tim. He's positive, he goes out there and plays his shots - that straight drive down the ground was one of the shots of the day. He's a cool guy to bat with," he said. "We just have some fun and have a laugh and try to stay as relaxed as we can. I'm fairly relaxed most of the time; nothing really fazes me, and Tim looks like he's pretty similar."

If England's middle-order slump can be considered familiar, so too can New Zealand's inability to squeeze their opponents when they're down. Yesterday, Daniel Vettori spoke of his frustration in their inability to close the deal, which is precisely what happened today. As in Wellington, New Zealand fed Ambrose's strengths outside his off stump. Fours were cut with fierce power time after time and, as admirably as O'Brien bowled - picking up career-best figures of 4 for 61 - they crave the firepower which Shane Bond once provided. They fought back to dismiss Ambrose and Pietersen in the dying overs but, as in the second Test at Old Trafford, the moment had gone. The momentum was with England.

In reaching 273 for 7, England have come within six runs of the highest score at Trent Bridge this season, but the cracks in their middle-order are still worryingly visible under the surface. South Africa will not let them off the hook so lightly, but then again, neither can anyone expect Pietersen to lift the throttle against his former countrymen.

Will Luke is a staff writer at Cricinfo