Durban - England are prepared for a South Africa backlash in the fifth and final one-dayer on Friday, said captain Andrew Strauss.
The visitors hold a 2-1 lead, after the first game was washed out by rain, but Strauss was wary of talking about a potential series win.
"It would be a bit naive to talk about series victories before we have actually achieved it," the opening batsman told a news conference on Thursday.
"We have to play well tomorrow(Friday) and have to expect another South African backlash."
England won the second and fourth matches by convincing seven-wicket margins, with the hosts claiming a comprehensive 112-run victory in the third game.
Despite the visitors being on the brink of their first one-day series victory in South Africa, Strauss believes his team are capable of better performances.
"I think we have progressed quite a long way but I am the last person to say we are the finished article yet. We still have a long way to go," he said.
Strauss said England had applied pressure on South Africa in this series.
"It doesn't matter how good a side is, if you keep putting them under pressure you are going to have success against them," said the left-handed opener.
"We have been able to do that a couple of times this series and let's hope we can do it once more."
South Africa skipper Graeme Smith feels his team have been below par so far.
"If we had played to our potential England would have had to take a few more risks up front while they were batting instead of us allowing them to play a certain way," said Smith.
"We haven't pushed them to perform under pressure and that is disappointing."