For some of us it happens when we earn our first paycheque. For others when we spend it on something we can truly call our own. For David Miller, it happened at Seddon Park on Sunday when he crafted a century from the ashes of a top-order collapse. As an international batsman, that was the day Miller grew up.

Let's be honest, 83 for 4 is not a place you would take a child to no matter who the opposition is. It could be dicey even for an adolescent who may be puffed up with false bravado. What you want at that time is an adult and luckily South Africa had one in JP Duminy. Since developing into an allrounder, Duminy's value to the team has increased volumes but there are some things even grown-ups cannot do alone.

South Africa's middle order has previously lacked maturity, even when it was made up of some of the most talented batsmen in the cricket world. Miller, who is among that latter group, has changed that.

He was in to bat before Duminy, a promotion that appears permanent, with his team on 67 for 3 at the end of the 17th over. Miller seemed in the mood to get a move on immediately when he sent the fifth ball he faced over cow corner for six but Elton Chigumbura asked for it when his attempted yorker went wrong. But 13 balls into his innings he had to press pause because AB de Villiers had been dismissed and South Africa were in trouble at 83 for 4.

Instead of mindlessly mauling an unthreatening but astute bowling attack, Miller had to play a defensive, observant game which seems the opposite of his natural style. It took him 38 deliveries before he coaxed his first four through extra cover and he only breached the boundary again 15 balls later.

His half-century was scored off 56 balls, hardly sluggish, but only 14 of those runs came in boundaries. Miller was grafting hard rather than going big and in so doing he was growing. "I haven't played as much first-class cricket as I would have liked to, but I've tried to work with what I've got," Miller said. "I've tried to play as much T20 as I can in the off-season, which is the only cricket I've been given a chance to play. I've been working really hard in the last two years to try and rotate the strike and build an innings. To try and take that into four-day cricket would be ideal."

International duty has limited Miller to just 11 first-class matches in the last three seasons including this one but in that time he has played 82 T20s. Of those, 59 were spread across three different domestic teams and Miller averages over 40 for all of them. His 1073 T20 runs for Dolphins, his South African side, have come at 42.92, his 1,086 for Kings XI Punjab include a century and have come at 49.36 and he has 457 runs from 14 matches for Yorkshire at 50.77.

Although those numbers have come in a condensed form of the game, they are indicative of the time Miller has spent at the crease working on his craft. He has learned how to construct innings so that by the time South Africa got to the 40th over on 193 for 4, unscathed but moving slowly, he knew what to do with the 10 overs that were left.

It was not quite what AB de Villiers had in mind. "We were talking about 240," de Villiers admitted. That would not have been enough.

Miller knew that when he changed gears. "David got a sniff in the 40th and just got going," de Villiers said. "We've seen him demolish attacks before. To see that at the highest level is great. It just shows you where this guy is going with his career."

Power-hitting is how Miller first came to the attention of the national selectors and he showed why as he helped Duminy plunder 146 runs off the last 60 balls and 30 in a single over. Miller's assault on Solomon Mire in the 48th over was what separated South Africa from a spirited Zimbabwe in the end.

"It was very fun. I had worked very hard leading up to that. I hit the first one for six and the second for four, and then I said to JP, 'I'm going to get you on strike', because he was sitting on 90 with two overs to go," Miller said. "JP said, 'No, just keep going; just go with it'. There was still enough time to get his hundred. So if it was in the area, I was trying to hit boundaries"

All six deliveries were in different areas - full, length, short, on the pads, outside off and even just right - and Miller hit all of them. Mire lost his composure and Zimbabwe were deflated. The magic wand a finisher wields is not just his bat but his ability to make it do something so sensational it shakes the opposition's strategies and bends them out of shape. It scars them. It stirs his own side. It sends shockwaves onto the scoreboard.

That's what Miller could always do. But the question of whether he could do that after doing all the sedate work that's occasionally required beforehand was only answered when his maiden ton came up three weeks ago in Port Elizabeth. Then, he had no substantial support and South Africa's day ended in defeat to West Indies.

Although a first international hundred is always a cause for celebration, like most batsmen Miller enjoyed his personal success a little less because of the team's collective failing. This time it was different. Not only did his hundred help South Africa win, but it was a victory in a major tournament. "To follow up with this hundred is really satisfying - to come out and do it in my first game in the World Cup," Miller said. "It was a matter of getting the team out of a bit of trouble." Just like a grown-up would.

Firdose Moonda is ESPNcricinfo's South Africa correspondent