In the space of a week, AB de Villiers has gone from captaining a team for the first time at any level, to winning an international series with two matches to spare. He'd be forgiven for thinking leadership is one of the easiest things he has been asked to do. But he doesn't.

Of all the players in the South African side over the past year, de Villiers developed the most. From a rough and tumble, schoolboy-style youngster as recently as during the 2011 World Cup, he has become a reasoning, sensible man whom anyone would want to call their captain. He also showed the ability to motivate, guide, think creatively and strategise, which are essential qualities for a leader of men.

"I am very proud of the boys. We took it one game at a time. I would like to think we will keep playing this kind of cricket," de Villiers said after the victory in Bloemfontein, which gave South Africa a 3-0 lead in the series against Sri Lanka. "We showed a lot of maturity, and a lot of young guys that came in showed experience. We didn't expect it to be 3-nil but we are very happy that it is."

South Africa managed to stay one step ahead of Sri Lanka even as the visitors took large strides towards improvement. The closest South Africa came to being caught was in Bloemfontein, but de Villiers lead the charge in a pressure situation to win despite wet weather. "The game was in the balance a little bit but I'm glad we got there in the end," he said.

One of South Africa's successful tactics was the rotation of the No. 4 position between de Villiers, JP Duminy and Faf du Plessis. In the third ODI, du Plessis came up the order and made his highest ODI score, 72, and de Villiers said they would keep the position fluid. "I warned you guys that we are going to mix it up a little bit," he joked. "I needed to bat down the order because it was important to get partnerships in the front."

du Plessis said he was "grateful" to get the opportunity to spend more time in the middle. "In the previous two games, I got two or three overs at the end so it was nice to go out and express myself." He also expressed himself in the field, where he effected a run-out to dismiss Kumar Sangakkara and saved lots of runs at point.

de Villiers also lauded a "much better" fielding effort by South Africa. Although they dropped four chances and missed five run-out opportunities, they caught four batsmen and ran out three others. de Villiers, however, said they had to improve and were not "a perfect team".

With the series won, de Villiers said the focus would be on "4-nil first" in Kimberley on Friday, because thoughts turn to a whitewash. It will also provide an opportunity to test new combinations, something South Africa started in Bloemfontein but can apply with more freedom in the remaining two fixtures.

"We could have one or two bowlers coming in but the batting will stay more or less the same," de Villiers said. South Africa had a new-look top three in Bloemfontein and de Villiers said they were likely to stick with that for the next two matches. "Colin [Ingram] deserves another chance at No. 3."

de Villiers also indicated that out-of-form batsman Graeme Smith would stay in the side, despite mounting criticism. Smith's last ODI hundred was during the Champions Tophy in 2009 and he has managed only one half-century in his previous 15 matches. With Alviro Petersen in good form, talk is rife that Smith will dropped once Hashim Amla returns from paternity leave.

"His [Smith's] confidence is not very high at the moment but I am expecting runs very soon," de Villiers said. "We know he is under pressure and we have to remember that no-one is invincible. Poor form is around the corner for all of us. But he is one of those big match players and he is old enough and experienced enough to know what to do. All we can do is support him."

Dale Steyn, Morne Morkel and Lonwabo Tsotsobe served South Africa well but two of them may make way for Vernon Philander and Wayne Parnell in the remaining games against Sri Lanka. Philander was brought into the squad after an injury to Rory Kleinveldt, but Parnell has been part of the group from the outset but has yet to get a look in.

Firdose Moonda is ESPNcricinfo's South Africa correspondent