Perhaps it was the nerves. Jos Buttler's fourth ODI hundred was also his slowest but it nevertheless provided England with the central pillar of their total of 399 for 9 in Bloemfontein and paved the way for them to go 1-0 up in the series.
Buttler's role in South Africa up to the start of the ODIs had been to understudy Jonny Bairstow as Test wicketkeeper. It had been two months since his previous competitive involvement, during the limited-overs leg of England's UAE tour, although he might have taken confidence from the fact his last ODI innings was a 46-ball hundred in Dubai, the fastest ever by an Englishman.
That put him on the radar of IPL franchises and, with the auction set to be held in Bangalore on Saturday, another blistering century - this time from 73 balls - will have done his chances of being picked up no harm. Perhaps the thought that he is on the verge of joining a select group of England players to be invited to the IPL party added to the sense of trepidation.
"I was really nervous," Buttler said. "Usually, I feel quite calm having played a few games with the experience. But I was really nervous when I got out there and I think that nervous energy showed in my innings. At times, I was trying to tell myself to hit the ball along the floor and take my time and then I'd play a big shot without really realising it. I think it was just the nerves that was making that happen. When your first big shots come off, I think that really settles you down and you immerse yourself in the game and the situation.
"I haven't played for a while," he added. "I finished well in Dubai but that is a long time ago and you're never sure if you can carry form forward. I've batted a lot in the nets but being in the middle is a completely different kettle of fish."
The quicker Buttler gets into the middle, the better for England, it seems. Buttler was again promoted to bat at No. 4 in Bloemfontein and having scored back-to-back hundreds in the position he now averages 115.00 at a strike rate of 172.93 there. Under Eoin Morgan's captaincy, England have adopted a more flexible - not to mention aggressive - approach and it certainly seems to suit Buttler, who has scored three centuries in less than a year.
He was ably supported by Alex Hales, Joe Root and Ben Stokes, who all scored fifties, as well as Jason Roy's pulsating 48 from 30 balls that helped set the tempo as England racked up their second-highest total in one-day internationals, and their highest overseas.
"We got off to such a great start," Buttler said. "The way Jason and Alex set up the innings, that allowed for Morgs to tell me to get my pads on. As soon as I was ready, we lost a wicket without really the thought about what to do and how I was going to play. When you get the promotion, you feel the expectation. You've been put up the order to continue the momentum of the two guys who started it and Rooty took on as well. You feel like you want to keep that going. That's the role I had to play after being moved up the order.
"It happened in Dubai as well. We got off to a good start and I was told to be ready to go in earlier. The great thing for our side is that we have flexibility. It might be we need a left-hander and Stokesy can go in and chance his arm. I think that is another strength of the side we are developing. Everyone is flexible and we have guys who can go in and play different roles in different situations."
Although South Africa were still in contention to chase down 400 when the rain arrived on Wednesday evening, it is England who are 1-0 up and looking to continue a freewheeling run in limited-overs cricket that has seen them smashing through self-imposed barriers in the wake of their World Cup exit.
"It gives us huge confidence to score nearly 400," Buttler. "This group of players, we've been challenging ourselves and pushing ourselves for a number of months. At times, we'll get it wrong and probably be all out for 280 in 40 over.
"But today is another great step forward for everyone to start this way in a series overseas against a very good team. It's brilliant, and we'll take this confidence forward. It's a shame the weather intervened, in what looked like it was going to be a really close match."
The IPL auction will be getting underway when England take on South Africa in the second ODI on Saturday. That might be another cause for nerves but Buttler is confident he will be able to tune out the noise until afterwards. "Obviously, I have no control over anything that is going on there. I'll be interested to know what happens but I think it will be pretty easy being involved in a full-blooded one-day international. That needs all the attention it requires."