It's easy to forget that Graeme Swann has only been a Test cricketer for a year. How did England ever manage without him? He has brought with him an infectious spirit and a joker-in-the-pack character, but today's performance with the bat, which bailed England out of a potential Test-losing hole, was surely beyond the bounds of even his confidence and self-belief.

Already Swann has a CV that includes two wickets in his first over in Tests, three five-wicket hauls, an Ashes-winner's medal and enough punchlines to fill a comic-book. Now you can throw into that list the fact that he is comfortably the best No. 9 in the world, and he could hardly hide his glee when he was told that Ricky Ponting had batted at the same position for Australia, at Perth, after being injured and made just 2. "How many did he get? Draw your own conclusions," he said during a typically chipper press conference.

Swann's Test-best 85 off 81 balls was England's best score by a No. 9 in 38 years, but still he couldn't resist. "I was kind of hoping it might be the highest ever," he said. "If I'd known, I'd have carried on pushing it round."

Joking aside, and it's sometimes difficult to do that with Swann, this was a hugely important innings. The team have a notoriously poor record at the beginning of overseas series - losing six out of their seven opening Tests - and a 150-run deficit would have left them nowhere to turn. Without Swann's intervention, England would have been praying for a highveld thunderstorm to save them, but now they are in a position from where victory is a realistic possibility. .

It wasn't just how many Swann scored, either, but how he made them. England have promised not to take a backward step in this series, yet at 221 for 7 they weren't making many positives strides forward either. Andrew Strauss will have had that sick feeling in the pit of his stomach; he'd put South Africa in, watched them score 400-plus, and then started seeing the pitch playing tricks.

Strauss, and England, are far from out of the woods yet - batting last will be a hazardous occupation - but what a difference the final session made. It was South Africa who left the field looking ragged and tired after watching Swann and James Anderson add 106 for the ninth wicket. South Africa's tail wagged by hanging around in the first innings, but England's had a far more forceful impact on proceedings which wrestled the match momentum.

"When Jimmy got cramp in his arm batting - the first time that's ever happened to him, I think - we saw Graeme Smith call a team meeting," Swann said. "He was fairly animated, so that obviously shows you're doing something right.

"You can tell when you're winding people up. The very fact that we're batting nine and 10 and put on a hundred, I know if I'd been fielding I'd have been calling us every name under the sun."

Swann even managed to unleash the switch hit against Harris, while Anderson registered his first six when he slog-swept the same bowler over deep midwicket. "It was a good crack - especially when Jimmy smashed that six," Swann said. "He was telling me shots I wasn't allowed to play - which I obviously did the next ball - and vice-versa.

"It's just great fun once you get going - and I'm happy that I've got a couple of switch-hits now, so I can show Kev (Pietersen) how to hit it along the ground."

Swann's innings continues his impressive Test form and follows an equally valuable 63 in the deciding Ashes Test. Three of his last four innings have been half-centuries, including a nothing-to-lose dash against Australia, as England slid to defeat in the fourth Test at Headingley.

"To go out there with a good mate of mine and put on a hundred and wrestle the initiative back our way is quite nice," he said. "It was certainly a game that was drifting horrendously out of our favour. Now, if we haven't quite got to a point of equality, we're pretty much back in the game."