South Africa captain Faf du Plessis bemused by team's loss to Sri Lanka

South Africa captain Faf du Plessis was at a loss to explain his side's surprise 2-0 home Test series loss to Sri Lanka, an unexpected setback for a team hoping to topple India as the number one side in the world.

Sri Lanka became the first Asian team to win a Test series in South Africa and ended the Proteas' run of seven home series wins in a row, after an epic one-wicket win in Durban and a convincing eight-wicket success in Port Elizabeth on Saturday.

"It's probably up there with the most disappointed I have been, certainly from a personal perspective but also for the team," Du Plessis told reporters.

"You don't want to be losing series at home, and obviously we didn't play our best cricket. It's a massive dent, I thought up until this Test series we were looking good. But credit to the team that played the best cricket.

"We were playing well, we were playing positive, aggressive Test cricket. But these last two Tests we were not on it as a team. I wish I can give you an explanation as to why."

South Africa's batting has been a concern for some time and failed again in the series, with a top score of 259 in their four innings.

The batting troubles have often been masked by a much-vaunted bowling line-up that has rescued the team on a number of occasions in Tests.

South Africa have passed 300 eight times in their last 28 innings, which includes being bowled out for 73 by Sri Lanka in Galle last July.

Their cause has not been helped by the seamer-friendly wickets that the team asks for on home soil, though Du Plessis refused to blame the Port Elizabeth pitch for their latest loss.

"There is no finger to be pointed at the wicket. Obviously, they (Sri Lanka) bowled well, but the biggest disappointment is the batting," the captain said.

"We have got some really good batters in there, but probably 99 per cent of the dismissals were soft judgement errors.

"When I was batting it felt like a really good wicket. In the first innings, there was a little bit of nip now and then, but it was a good batting surface."

World Cup

The makeup of the South African one-day international side is different from the Test team, but Du Plessis said they don't want the disappointment of the series loss to hinder the 50-over team just months out from the World Cup in England.

"There is a big five months coming up, so for us it's making sure that you never take your preparation for granted," he said.

"If you see the guys starting to slack a bit in terms of that then you address it as soon as possible because that is the one area you can control.

"The guys should be very motivated for what is coming up, it is one series and then the World Cup."

South Africa and Sri Lanka will next contest a five-match ODI series that starts on March 3.