Momentum is a peculiar and unquantifiable beast in sport, but it's fairly easy to pinpoint where it lies at any given time. In this series, it has transferred sides in the space of a week. Last Saturday evening South Africa had been made to follow-on, yet seven days later they have built a lead of 119 with the potential of plenty more to come. However, while the script has changed, one of the central characters has remained the same.
Ashwell Prince is the type of batsman who could easily have slipped under England's radar this series. He is that solid buffer in the middle order between the modern-day greatness of Jacques Kallis and the supreme natural talent of AB de Villiers. But if England's attack didn't know much about him before this series, they are more than familiar with his skills now. Hundreds in back-to-back Tests have left an indelible mark.
"We all know that over the last few years he has been a star performer and done really well," said Hashim Amla, who batted alongside Prince early in his innings. "I think his temperament is superb and he keeps the game quite simple. That's his biggest trait, he has a game plan and he sticks to it. He's playing well at key occasions, three wickets down and produced two fantastic knocks. Two of the best I've seen from him."
Prince's 101 was a superb innings, but even he admitted the gloss was taken away by the team's position on that Saturday as they were made to follow-on. In hindsight, he more than played his part in the match-saving effort, but he can rest easily tonight knowing that he has put his team in pole position.
It shows the value South Africa gained by escaping with the draw at Lord's. They could, in effect, start the series afresh here in Leeds, but with the knowledge and experience gained from the first Test. "At Lord's we didn't apply ourselves very well [in the first innings] and were overwhelmed by the occasion, but that's just excuses. Now, with one Test down, we are battled hardened."
Maybe it's because he doesn't possess the record of Kallis or the thumping brute force of Graeme Smith, but Prince doesn't immediately spring to mind as one of South Africa's key players. Yet, that could just be the secret to his success. He quietly goes about his role in his own style and has more Test hundreds than fifties, which confirms his appetite for making the hard work count. The Prince of the last two Tests also hasn't been afraid to show his full range of strokes. When Monty Panesar came into the attack, at a time when Michael Vaughan was looking for control, Prince twice put him straight down the ground into the stands. There was no doubt where the momentum lay.
South Africa have done a good trade in gritty left-handers since readmission. Kepler Wessels was as tough as they come during their early years, then the mantle was passed to Gary Kirsten. Five years ago at Headingley, Kirsten played one of his finest innings when he made 130 with the ball zipping around and South Africa limping on 21 for 4. Conditions here were nowhere near as tough for Prince - the opening day cloud had dispersed, which makes a huge difference at Headingley - but the closest he came to offering a chance was an inside edge past leg stump off Panesar and a late flash over the slips off Stuart Broad.
There were question marks over Prince coming into this series after a lean period towards the end of the South African season and in Bangladesh. He was on the original roster of IPL players, but none of the franchises fancied his services in the first auction and it wasn't until later he eventually went at a bargain-basement price (by IPL standards). Meanwhile, Prince's team-mates such as Kallis, Smith and Mark Boucher went for mega-bucks. But even though he may not have had huge kudos in the Twenty20 world, his value to South Africa's Test side is growing.
His standing within the team has never been in doubt. He is the vice-captain, ahead of more senior colleagues like Kallis and Boucher. Prior to the series Smith spoke about the closely-knit unit that he has finally been able to form and Prince is a key part of that.