England captain Joe Root has warned his side they can no longer afford to play their best cricket when they are backed into a corner.

Root saw his side slip to a 107-run loss in the first Test against South Africa as their hopes of hunting down a record fourth-innings chase of 376 fell well short in Centurion.

The tourists were dismissed for 268 on the fourth evening, a creditable effort on an uneven pitch and against a highly-motivated Proteas attack.

It certainly outstripped their day two effort of 181 all out, when they lost their last seven wickets for 39 to surrender control of the match and goes down as the latest instance of Root's Test side doing their best work when in a hole of their own making.

Against Ireland at Lord's, when they bounced back from the depths of 85 all out, and in the miracle of Headingley when Ben Stokes reeled in a target of 359 against Australia, that was enough. But no more.

"I think the thing that's frustrating me is that, when we find ourselves behind in the game, we show a lot of character, fight and determination and we find ways of getting ourselves back into things," said Root.

"In terms of character over the last two days, I can't fault anyone. We turned up with real belief we could win the Test. Even at lunch me and Ben looked at the scenario and it was the same equation as Leeds not so long ago.

"But we need to do that at the start, get ahead of it. When we get the opportunity to turn the screw, we really need to take it. That's where the game was won and lost this time round, the first innings with bat and ball."

Root did not cite the bug which was spread through the camp as a reason for defeat, though nor did he downplay the effect it has had on preparations.

He fell ill and was forced into quarantine as the game drifted away from England on day three, with another nine squad members and four backroom staff suffering symptoms since arriving in Johannesburg a fortnight ago.

Three were ruled out of the Test entirely and others went in light on workload. As attentions turn to the second Test at Newlands, Root simply hopes for an end to the medical bulletins.

"We're not going to hide behind that as an excuse, but 14 of our squad have been taken ill in the last week and a half," he said.

"We've had a lot thrown at us and everyone has dealt with it the best you can. It's frustrating, but it's happened. Hopefully the illness is through the camp and we can all be fighting fit in time for Cape Town."