"On [Mohammad] Ashraful's day, no team is safe. Not Australia, and now, not South Africa" © AFP

Rankings? Tear them up, throw them away. That's what Bangladesh can say now, with some justification, after South Africa, the world's No 1 side, was comfortably dispensed with by the a team ranked ninth.

The two teams are relatively new to each other, and their previous mutual history is the story of Bangladesh's helpless capitulation. In seven previous matches, only once had Bangladesh crossed 200; their best performance saw them lose by 83 runs. South Africa had acquired the status of a spectre; on Saturday, the tables were effectively turned.

Saturday's match, the Guyana Epic, may well be considered Bangladesh's best-ever one-day performance. Not just because it was their first-ever win over South Africa; not because South Africa are the world's top-ranked team; nor even because this result has thrown open the Super Eights, and brought this tournament to life. This was Bangladesh's best-ever result because they reduced South Africa to the same shambolic mess that they would usually find themselves in.

Over the past three years Bangladesh have acquired the reputation of being giant-killers; Australia, India, Sri Lanka - and India again during the World Cup - but in none of these matches was victory so emphatic. In none of these matches was the conclusion just a ceremony, as it was on Saturday.

Bangladesh has stunned this World Cup - stunned the world. Maybe even itself. Yes, Bangladesh had threatened a couple of upsets soon after ascending to the Super Eights. But the first two matches against Australia and New Zealand had caused some of the confidence to evaporate.

Before the South Africa match, though, Bangladesh was singing its familiar tune. At the press conference on Friday, Habibul Bashar, the captain, was asked directly: What did he expect from the match, a win or a fight? Habibul had said he wanted to fight. There wasn't much of a fight yesterday - but Bashar wouldn't have been complaining. Bangladesh are now a dangerous side; predictions involve playing with fire.

Graeme Smith, the South Africa captain, wrote on the eve of this match in his column for Prothom Alo that his team would not repeat India's mistakes. But it wasn't enough for South Africa not to want to make mistakes. Bangladesh compelled them to go wrong. The opening pair scoring 42 runs in 13.4 overs; losing three wickets by the 20th over with 69 on board; just 92 runs in 25 overs - Smith could not have imagined this match would be the biggest embarrassment of his captaincy.

It goes without saying that the credit for bundling out South Africa - who have successfully chased 400 - for 184 goes to the bowlers. Yet the edifice for the win was built by the batsmen. Instead of batsmen, we can say Mohammed Ashraful. His 87 off 83 balls is a reminder that on Ashraful's day, no team is safe. Not Australia, and now, not South Africa.