England must sort batting top order - Jonathan Agnew

Nick Compton (left) and Alex Hales
Nick Compton and Alex Hales made 381 runs between them in 16 innings, while Hashim Amla made 470 on his own in seven

England seem set to end the series in South Africa with a defeat after a horrible start to their second innings.

They quickly subsided to 18-3 and you feel something exceptional will need to happen from the overnight score of 52-3 to prevent a heavy loss, with a victory target of 382 surely entirely academic.

South Africa's pace attack exposed some familiar weaknesses but also highlighted that the Centurion pitch is very difficult, especially with the new ball.

There was pressure on; the light was not great; England couldn't win the game; they were batting to save the game - all the usual issues.

You might think that England should have fared a bit better but the new ball is difficult.

Leading England run-scorers in the series
401: B Stokes - 7 innings, average 66.83, highest 258
385*: Joe Root - 7 innings, average 64.16, highest 110
345: J Bairstow - 6 innings, average 86.25, highest 150*
245: N Compton - 8 innings, average 30.62, highest 85
184: A Cook - 8 innings, average 23.00, highest 76
181*: J Taylor - 8 innings, average 30.16, highest 70
136: A Hales - 8 innings, average 17.00, highest 60
106: M Ali - 6 innings, average 26.50, highest 61

It's very awkward as a batsman when the ball lands in the same place on separate occasions and does completely different things.

Captain Alastair Cook got one that rolled along the ground and another that nearly took out his armpit, and when you've got about half a second to react and in your mind you're wondering what the pitch is going to do, that creates uncertainty.

Top batsmen have to deal with these situations but it is so much easier said than done.

Alex Hales got one that kept a bit low but it was another failure.

He has had four games and scored 136 runs. My view has not changed: any opening bowler would reckon Hales gives you more chance than he should as an opening batsman.

It's possible they will continue with him. They dropped Adam Lyth after seven matches, and they are running out of options as to who to turn to with eight opening batsmen tried since Andrew Strauss retired in 2012.

They could put Nick Compton up there but he has hardly set the world on fire, either opening or at number three, and he played a loose shot to be the third England wicket to fall inside the opening 10 overs.

They are going to have to think hard about it, but they have got to sort the opening position out.

In the early summer conditions when England play three Tests against Sri Lanka, Hales might well score some runs and it might just be that one score that gets his Test career under way. But he just has these technical issues that have been talked about time and again.

He has got one score of 60 but the other innings he hasn't got going and it will be the manner of the dismissals that will disappoint him.

But pressure makes you do funny things and Hales, Compton and James Taylor all know their places are under the microscope.

Discarded players such as Gary Ballance and Ian Bell will be thinking that if they start the domestic season well they could force their way back into the team.

Cook's opening partners since Andrew Strauss retired
MatchesRunsAverage
Root533937.66
Compton947931.93
Robson733630.54
Carberry528128.10
Lyth726520.38
Moeen38414.00
Trott37212.00
Hales413617.00

All of these players will feature in county cricket and will have a few games early-season. They will have to get out there and battle to earn selection.

It is no bad thing in a way; you want competition for places and you want it to be tough but I don't think any of them will be sleeping particularly easily before the selection for the first Test match against the Sri Lankans at Headingley on 19 May.

I would be surprised if they went back to Bell, though. It seems as though they have moved on after he was part of the 2-0 defeat against Pakistan in the United Arab Emirates late last year.

Ballance has made four hundreds and six fifties in his 15 Tests and I think they want to get him back in the side again, but he has got to earn it.

Promise for South Africa

Having lost the series, South Africa are ironically now enjoying some players in excellent form, so they have a great deal of hope for the future.

Hashim Amla played beautifully again. It was a very brave innings after being hit a few times on the thumb and it was a shame he didn't get his second hundred in the match

South Africa batsman Temba Bavuma
Temba Bavuma averaged 49.60 from his seven innings in the series

And the diminutive Temba Bavuma, who made that wonderful hundred in Cape Town, continues to impress everybody.

He's got an excellent attitude, he moves his feet really well, technically he looks good and he has been a revelation, as has the young fast bowler Kagiso Rabada. He took two more wickets to tear through the England top order in that short session before the close.

They both came with promise but have really shown they can have really successful Test careers.

It's a big day for Rabada, who wants one more wicket to become the youngest South African to take 10 in a Test match.

I wondered how he would run in having bowled 29 overs, getting his seven wickets in the first innings haul of 7-112, but he certainly seemed to be moving OK.

He will do that I am am sure, and he and Morne Morkel will be quite a handful.

Clearly South Africa will be very strong favourites to wrap it up on the final day.

I was a bit surprised how long they batted on. I thought they would have got to a 270 lead and really push on and play more shots.

Had they declared earlier they could have had England batting before the storm arrived and tested them in some very dark conditions.

AB de Villiers is a new captain and it is always difficult setting up declarations, but the general view is they could gave declared an hour earlier.

However, they've got lots of time left and they have the second new ball, which is perfectly timed after 60 overs on Tuesday to wrap it up if they haven't already done so.

Jonathan Agnew was talking to BBC Sport's Jamie Lillywhite.