"We have put in two and a half months of hard work and thrown it all away in a couple of days, which is very disappointing," Illingworth said. "We should have made at least 250 in the first innings. The outfield was slow but 250 to 300 would have been a fair score on that pitch.
"We played a lot of irresponsible shots. Test matches are not won like that. At Centurion Park in the first Test, we grafted. That's what we had to do on this pitch and we didn't do it.
"I thought when South Africa were 171 for 9 in their first innings that was our best day in the field of the series. But we were a waste of time with the new ball.
"We blew it. If we had restricted them to a lead of 20 or 30 we would have been favourites."
Asked about the umpiring during the day, Illingworth replied: "We had some so-and-so decisions today. I don't want to say any more than that."
Illingworth insisted that England are progressing along the right lines - despite another series defeat.
"We have made progress in certain areas. I think we have the nucleus of seven or eight players. We have two or three players from the A team who will certainly come into the reckoning," he said. "We will go forward with youth. I wouldn't go as far as to say that some of this team have played their last Test but there will certainly be one or two changes."
Mike Atherton blamed his team's batting for the failure. "We battled hard for much of the series. We played well in patches. But we didn't bat well enough as a unit, as a team, to win the series. Too many of our batsmen will look back on a disappointing series," the England captain said.
"I was very happy with this squad when we came out here. I thought it was a fairly youthful squad. I thought the composition was good. In the end, not enough individuals had a good series to turn it our way. But if I'm still captain next summer, I would not envisage too many changes."
Ian Botham, one of Atherton's predecessors as captain who was summarising the match for Sky, said: "We really do need another strike bowler of quality. South Africa had the edge with Donald, Pollock and McMillan. They have rarely wasted the new ball and always had England's top order under pressure."
Donald was named both the man of the match and the man of the series.Reuse content