England must improve dramatically to save their world number one status after being outclassed by South Africa in the first Test, Bob Willis told Sky Sports News.
The hosts lost by an innings and 12 runs at the Oval - a remarkable turnaround after ending day one on 267-3.
England dominated the Proteas' attack on Thursday but the following four days saw Graeme Smith's side take the upper hand, with a fine batting display from Hashim Amla (311 not out) at the heart of the tourists' resurgence.
"It all went wrong from the end of the first day," said Willis. "Who would have predicted such a humiliating defeat after they were 267-3 at the end of day one?
"But South Africa bounced back and showed their professionalism, determination and class - and England were outclassed in every department
"There are now some cracks in this invincibility of England and the fact is they have lost five of their last nine Test matches.
"That is not the form of the world's number one side and in a three-match series, they are going to have to work devilishly hard to get back on track."
England's much-heralded bowling attack managed to take just two wickets in the match and Willis said, regardless of the benign track, the hosts' bowlers must show more threat.
He was critical of England's batsmen, too: "This is the first time England's bowling attack hasn't performed for about two years.
"When the batsmen were fouling up in the United Arab Emirates and Sri Lanka, the bowlers at least were taking wickets on a regular basis - but on this flat Oval pitch England didn't have any venom at all.
"The most worrying thing to me was that Stuart Broad was bowling at under 80mph. On a pitch like that you've got to bowl with pace. They didn't have that.
"But South Africa's Morne Morkel and Dale Steyn were able to run through England - with the help of some very irresponsible shots from England's batsmen.
"The shot selection from England's batsmen was very disappointing, particularly at the start of the second day, when those wickets were tumbling down and England still have a problem at number six.
"They've tried Eoin Morgan, they've tried Jonny Bairstow and now they're back to Ravi Bopara. It doesn't seem to be working for any of them. They don't seem to have the temperament for the game at the top level.
And, to be honest, the shot selection from some of England's experienced batsmen in the second innings was absolutely woeful."
The same could not be said for Amla, whose innings left Willis immensely impressed.
"It was a wonderful innings from a wonderful player and a wonderful guy," he said. "He's so self-deprecating but this was world-class batting against a much-vaunted bowling attack. He never looked in trouble during that whole stay.
"Graeme Smith laid the foundations and Jacques Kallis - statistically the best all-rounder the game has ever seen, with 300 wickets and an average of nearly 60 with the bat - was superb.
"South Africa have four batsmen in the top 10 in the world rankings and they showed why they're up there. Alastair Cook is the only batsman England have in the same echelon."
The series had been talked about as a showdown between Steyn and Anderson - but there was only one winner of that contest in the first Test, says Willis.
"This was billed as the great contest between Steyn and Anderson before this series began, number one and number three in the world, respectively. I'm afraid it's been a first round knockout for Steyn over Anderson," he said.
However, Willis believes England do have the ability to come back from the heavy defeat at Headingley next week - but reckons it will be hard work.
"There's plenty of work for England to do," he said. "They're very resilient and they usually bounce back after a heavy defeat. I'm sure they'll stick with the same squad - but they've got to perform a whole lot better.
"There's usually a result at Headingley and England have had some easy victories there. They beat West Indies there in two days, not so long ago. But they also lost by an innings to a poor Australia side two years ago as well."