'It's been one of those happy days' - Strauss

It's never been easy to spot what makes Andrew Strauss tick. The same phlegmatic attitude that carried him to an incredible tally of 10 hundreds in his first 30 Tests has made his subsequent failures all the harder to pinpoint. He's not seemed especially out of form in any of his 16 Tests since Headingley in 2006, the scene of his previous Test century, but that's because even when he's been at the top of his game, he's not been one for getting carried away with the moment.

Today, however, was different. The roar of relief and the punch of the bat that greeted his career-saving century betrayed the pent-up anxiety that had accompanied it. After that sort of release, the rest of his day was plain sailing. "It's been a pretty long time coming," Strauss said. "There was a lot of emotion, a fair amount of relief and a lot of joy to be contributing again. Just to see the ball go away through the covers, it's been one of those happy days you enjoy."

Strauss's struggles have mirrored his team's decline. His debut, against New Zealand at Lord's in 2004, marked the start of his team's run of seven home Test victories in a row - a clean sweep that paved the way for the heroics that followed against Australia the following year. His omission for the recent tour to Sri Lanka came at the end of England's 1-0 series loss to India, their first home defeat since 2001.

He was then recalled for the New Zealand tour on flimsy evidence, through the failings of others rather than any successes of his own, but it was arguably his post-lunch dismissal on the second day in Hamilton that triggered England's defeat in that game. After a top-score of 44, and a duck in England's first-innings collapse here, axes were being ground, and Strauss' scaffold was visibly being erected as he walked out to bat for this innings.

Mentally, however, Strauss was two steps ahead of the executioners - a situation that had not been the case last summer. "Once I got left out of the side for Sri Lanka, I made a conscious decision not to think too much about what's happening in the next Test," he said. "Once I got back in the side, my goal was to enjoy each Test and play almost as if it's your last. The negative thoughts do come into your mind, but you try to push them right to the back and just enjoy yourself."

"You never know when the last Test will come," he said. "Prior to Sri Lanka I was thinking too much about what might happen. It was just a question of going out on a pretty flat wicket and applying yourself. Some days it's your day, some days it isn't."

Today simply had to be Strauss's day. The stage was set for a series-defining innings, and he was ready to deliver some overdue promises. The hard work of his innings had arguably been done on the previous evening. On a crazy day in which 15 wickets fell, Strauss had arrived in the middle early following some poor shot selection from his captain, Michael Vaughan. By the close, he had eased to 42 and eaten 30-odd overs out of the new ball. As soon as the sun appeared high in the sky this morning, a familiar and long-forgotten sense of certainty flooded back into his play.

"I know I'm a good enough player to score Test hundreds, and it's just a question of getting the opportunities and taking them if they arise," Strauss said. "On a decent wicket like that, you just have to keep your emotions in check and keep in your little bubble. Both sides have been guilty in this series of giving the opposition a chance, and we really didn't want to do that today."

That's what Strauss in particular has been guilty of in recent months. Uncharacteristic rushes of blood have coloured his cricket, ever since he played himself into a trough during last winter's Ashes. He painted himself into a corner with a pair of rash pull shots in Brisbane in the opening Test of that series, while his last opportunity for a hundred was scuppered at Lord's last summer when, on 96, he charged down the track to Anil Kumble and shovelled an edge to Rahul Dravid at slip.

The Strauss of old never, ever, did anything so rash. His incredible run of form in South Africa in 2004-05, when he made 656 runs including three centuries and top-scores in seven of the first eight innings, was compiled through an acute awareness of his limitations and an insatiable desire to cash in when possible. The cut and the drive were his staple shots, with a dash of the pull shot when the going was good. Today's innings wasn't quite so clear-cut, at least not until those elusive three figures had been raised, but it was a definite step towards salvation.

"That's the key to good batting, knowing what your game is and sticking to it," Strauss said. "I was sometimes a little bit scratchy, but I'll never be a Kevin Pietersen-type player who spanks it all over the place. I try to play the ball as late as possible, and after I got my hundred I certainly felt more comfortable, and was getting into better positions. Sometimes a little thought will come into your mind, saying: 'I can hit him over the top' or 'I could do this or do that'. But you've just got to keep in your bubble and play the percentages. Today that happened to me."

Strauss's most significant moments of anxiety came on 97, when New Zealand handed the new ball to Chris Martin, who beat his outside edge four times in a row. "It's worse when you're on 0," said Strauss, an opener by trade. "But it was one of those things. The spinners had been on before the new ball, and I had been thinking I might try and get it out of the way. But then I thought back to India [at Lord's] last year, and I thought no, I'll just play the percentages and wait for the right ball. Thankfully it came along."

His place in the side is secure for the foreseeable, and the phlegmatic mentality is slotting back into place. The next stop for Strauss - before England declare and push for victory - is to cash in on the moment, and turn his overnight 173 into a landmark to remember. "We'll have a chat in the morning, and I'll just keep batting if I can," he said. "I was frustrated in my previous hundreds that I didn't go on to get a big one. But after 30 innings without [a hundred], you can appreciate that these runs now are the easiest to score." That's more like the Strauss of old. Right now, he's back to scoring runs for fun.