George Dobell is a senior correspondent at ESPNcricinfo
It is one of the oddities of England's cricket of late that, despite having a template for something approaching the perfect opening batsman in Alastair Cook, they persist with the theory that his opening partner should be completely different.
Cook's virtues - his patience, his compact technique - were in evidence here. In circumstances in which England sorely needed the solidity he offers, he provided a masterclass in opening the batting: he left well; he retained concentration and, if the bowler dropped short or over pitched, he punished them. He will resume on Sunday requiring 50 more runs to become the first England player to reach 10,000 in Tests.
But England continue to search for the right partner for him. Alex Hales, the eighth man to try since the retirement of Andrew Strauss, is now averaging 19.28 in this series. His dismissal here, half forward and slicing a drive to point, was worryingly familiar: it is now five times in seven Test innings that he has lost his wicket pushing at a ball outside off stump. It is a mode of dismissal that speaks of poor footwork and fragility out off stump. Those are serious issues for a Test opener.
Hales, though, has been encouraged to be positive. Like Adam Lyth before him, he is a naturally aggressive player who has built his reputation largely upon his strokeplay. They might be termed England's answer to David Warner or Virender Sehwag.
Only they aren't as good. So they have to learn to play within their limitations which means learning, like Cook, to leave the ball outside off stump with far greater confidence. To see Hales dismissed twice in the warm-up games leaving straight balls was to see a man who was not secure in the location of his off stump. And if that is the case, it is almost impossible to make it as a Test opener.
Like all who preceded him in the role of Cook's partner, Hales is a fine player. He has, in recent times, scored big centuries against arguably the two best attacks (Yorkshire and Warwickshire) in county cricket and he has already recorded centuries for England in T20 and ODI cricket. Whatever happens here, he has a future in the white-ball game.
It is true, too, that if England persist with him for long enough, he will score runs. The issue is whether he will score runs consistently enough to make a success of the role of opening batsman. Only once in his seven innings has he batted for two hours - the length of a normal session - and that came on flat pitch at Cape Town on which both sides made more than 600.
That should not surprise us hugely. Sixty percent of his first-class innings in 2015 were ended before he reached 25. That compares to 45% for Nick Compton and 38% for Michael Carberry. He is a dangerous, elegant cricketer. But he has always been hit or miss and asking him to step up to a higher level and discover consistency is unrealistic.
That does not mean he should necessarily be dropped. England have tried so many options at the top of the order and, until either Tom Abell or Daniel Bell-Drummond are ready, there are no obvious options that have not already been tried.
Lyth and Sam Robson - both of whom could return - were given seven Tests each to make the role their own. The difference with them was that they scored centuries in their second Tests; Robson against Sri Lanka and Lyth against New Zealand. Perfectly reasonably, that brought them an extended run in the side.
Hales made the admirable decision to forgo a chance of IPL riches to give himself the best chance of making a success of the role of Test opener. He will, therefore, play for Nottinghamshire in the opening weeks of the season - and opening at Trent Bridge in April is desperately tough - rather than entering into the IPL auction. If he does well, there is no reason England will not select him for the first Test against Sri Lanka.
He has not looked completely out of his depth, by any means. Even in this innings, he followed a pleasing cut with a beautiful drive off the back foot and his defence on off stump has looked good. It's just he keeps being drawn into those pushes outside off stump. If he can improve that, he may yet have a future at this level.
It says something for England's plight in this regard that only three opening batsmen have had a lower average in a completed series (with a minimum of six innings) for England since 2000 than Hales. All of them - Moeen Ali, Jonathan Trott and Adam Lyth - played in 2015 and were Hales' immediate predecessors. Clearly, county cricket is not producing the quality of opening batsmen it once did. The likes of Martin Moxon, Bill Athey, Chris Broad or Kim Barnett - men who enjoyed only brief international careers - might be considered an automatic selection had they been playing now.
England's opening issue is not their only trouble. By the end of the South Africa innings, Jonny Bairstow had the unwelcome distinction of having missed chances off all three centurions. If a Test wicketkeeper has ever done that before, it is unlikely they played the next game.
None of the chances were especially simple. But one of the characteristics of the best players is that they make the tricky appear straightforward. Bairstow has the opposite characteristic in his keeping. His footwork is so far off the pace that he makes most catches appear harder than they might.
"We'll look back on this game and realise we let them off the hook massively," Ben Stokes said at the end of the second day. "We were the ones that let them get to the big score.
"You can't give a player like Amla chances. He really made us pay for the fact that we dropped a catch. We've got to take those chances. Good players make you pay and they certainly have in this innings."
Bairstow's batting has been excellent; his hard work and good intentions cannot be doubted. But he is, right now, some way below the standard required for this level and judging by the reaction of some of his team-mates during the day's play, the level of frustration is growing. The place for learning these skills is county cricket; not a Test series against a side that began the series as world No. 1.
"It's just a case putting it behind you and making sure you take the next one," Stokes said. "But unfortunately this innings Jonny didn't manage to take the chances. But on another day he could possibly and it would be a completely different ball game.
"There's no grudges held but at the same time there's no going up and saying 'catch the next one' because that's just a cliché thing to say."
It may be that the solution to both England's most pressing issues - their keeping and their top-order batting - can be combined. If Compton, who was dismissed here by a ball that kept impossibly low, were to be promoted to open the batting and Bairstow were promoted to No.5, there could yet be room for a more assured keeper.
Ben Foakes, who has the ability to develop into a decent batsman, might be the long-term option but Surrey really need to be persuaded to do the right thing by England cricket and hand him the gloves as much as possible as soon as possible. It is worth noting that, in the five innings in which he kept in the County Championship last year, he completed three stumpings. Gary Wilson, who kept in 23 innings, completed one.
South Africa vs England
England tour of South Africa