When Rory Burns was forced home, just as the second Test started, there was trepidation over how England would cope.
At that stage, Dom Sibley was averaging 14.20 after three Tests, while Burns' replacement, Zak Crawley, had scored only one Test run. It was as young, green and unproven an opening pair as England had fielded for many, many years.
But it is amazing what happens when opportunity is offered. And now, just two-and-a-half Tests later, Sibley has a maiden century and Crawley has improved his career-best score for five innings in succession.
Perhaps more importantly, the pair have started to do what other aspiring pairs have failed to do for many years. They have taken the shine of the ball, forced bowlers into second and third spells and built foundations on which the middle-order can build.
The most obvious example of that came on the first day in Johannesburg. By registering a century stand, they not only gave their side a foothold in this game, but made a decent case for their retention - for Sri Lanka, at least - as England's opening pair.
If a century stand sounds like a relatively modest achievement, it is worth reflecting on the statistics. It has been more than three years since England last enjoyed a century opening stand - it was between Alastair Cook and Keaton Jennings in Chennai in December 2016 - and 10-and-a-half years since they enjoyed one in the first innings of a Test. On that occasion, in July 2009, Cook and Andrew Strauss were the opening pair. It is rare, too, to see one on this ground: the last made in the first innings of a Test was 2003; the most recent in any innings was in 2013.
So these are significant indicators. And bearing in mind the age of England's opening pair - Sibley is 24, Crawley is 21 - and the struggles of the many men who have gone before, it may be worth investing in this pair a little longer before making any change.
Burns, it should be remembered, will not be available for Sri Lanka. And while there is talk to recalling Jennings, the selectors may also reflect on the rate of improvement in this young pair and conclude that it would be unhelpful to separate them now.
It was Crawley's innings that made the biggest impression on Friday. Nicely though Sibley played, he has already made a century and there is no longer any sense of surprise when he establishes himself. He has now scored at least 29 in his last five Test innings. And again, if that sounds modest, remember that South Africa said they would have bowled first had they won the toss and this is, arguably, the fastest surface in the world.
Crawley, though, looked calm, confident and classy. It's not just that he blunts the attack; it's that he has the weapons to hurt it. He can drive off front and back foot, he can cut, he can pull and he's murderous off his legs. The wagon wheel of his 10 fours underlines this: four came on the on side; four came on the off; two were straight. All 10 were in front of square. On a quick pitch, that's remarkable and suggests an unusual amount of time to play the ball. Cook, by comparison, would surely have scored very few of his boundaries in front of square.
But most of all, Crawley showed excellent judgement in which balls to leave which is essential on this surface. All four wickets so far have fallen to edges behind the stumps; the ability to leave on length as much as line suggests Crawley has what it takes to succeed at this level. You suspect he is coming to the same conclusion.
"I've definitely got a lot more confidence in myself," Crawley said after play. "I wouldn't quite say settled yet. I've a lot more to prove. But I feel if keep improving - and I feel like I'm improving quite a lot each game - it will not be too long before I feel much more comfortable.
"I've definitely learned a lot mentally about playing the best bowlers in the world and seeing them off. When to attack and when not to. When I got out the way I did to Kagiso Rabada in Cape Town, he only had a couple of overs left in his spell. The people who think the best in this game are the best players. So I'm trying to learn a lot from Ben Stokes and Joe Root who score a lot of runs for England."
The one concern might be that he was hit by a bouncer from the enduringly excellent Anrich Nortje. While Crawley played the incident down, it will have been noted by fast bowlers in Australia, in particular. He is a big man - every bit of six feet, five inches - and tends to take the short ball on. There may be times that combination proves a dangerous one.
As an aside, that incident showed up a potential flaw in the protocols regarding the changing of helmets after such a blow. The England camp took a while to find a suitable replacement helmet - partly because Crawley had a lump on his head - and the umpires threatened to retire him hurt unless he accepted an ill-fitting one. While their eagerness to progress the game is admirable, such impatience could encourage players to wear ill-fitting protective equipment. And that could have dire consequences.
"I can understand why," Crawley said. "It did take quite a while. I had to wear Dom Bess' helmet until tea. Luckily he has a big head. If I was on the fielding side with that short amount of time before tea, you'd want to have another crack at a batsman who has just been hit. But I can't bat in a helmet too small for me."
On the face of things, Joe Denly has experienced a similar series to Crawley. His average (33.66) is similar to Crawley's (34.75) and they have both scored one half-century. But beyond the raw stats, it feels as if they are having very different experiences. As if one career is in the ascendancy and as if the other is fighting to remain afloat. And with Burns to come back at some stage and talk of England using Jonny Bairstow at No. 3 in Sri Lanka - he scored a century from that position in the last Test England played there just over a year ago - it may be that competition for places is becoming much tougher.
Denly has, in many ways, performed admirably for England. He has fought, he has occupied the crease and while he has failed to register a century in his 13-and-a-half Tests, he has worn down attacks. But his innings on Friday was not atypical of his Test career: he was dropped twice - the seventh and eighth time in his Test career he has benefited from a reprieve and the sixth time he has benefited before he has reached 20; no-one else in the world has been dropped so often over the same time frame - and he survived two inside edges that whistled past the stumps.
In short, while it feels as if Crawley is playing within himself - forcing himself to leave balls, but showing the ability to hit all round the ground - it also feels as if Denly is stretched to the limit to survive and enjoying a disproportionate amount of fortune. Several England No. 3s of a previous era may look at his career average of 30.88 and wish they had benefited from such patience. Crawley, 12 years younger, has further scope to improve and learn. Does Denly, at 33?
If Burns were available for the next Test, it is surely Denly who would make way from the top three, not Sibley or Crawley.