It was on the back of "one or two mistakes" against England and West Indies that South Africa's campaign turned sour, said Faf du Plessis after his team had secured victory over Sri Lanka. South Africa failed to defend 229 against England, then scored only 122 for 8 against West Indies, despite having come to the World T20 as one of the favourites.

They were comfortable victors against Sri Lanka, however, restricting the opposition to 120 for 8, before running down that total with eight wickets and 14 balls to spare. As a result, South Africa finished third in Group 1, ahead of Sri Lanka and Afghanistan.

"We played good cricket leading up to the tournament and we were consistent in the subcontinent, but a World T20 is a do-or-die tournament," du Plessis said. "If you make mistakes, it's not like a series where you can come back into the series. We made one or two mistakes against England and they punished us for it. Against West Indies, we made one or two mistakes as well. The teams in a T20 world cup are so close to each other, if you're not on top of your game, teams will punish you. Tonight was a good example. Sri Lanka made one or two mistakes in their batting, and we capitalised."

Sri Lanka had moved to 45 for no loss in the fifth over, before Aaron Phangiso claimed two quick wickets to slow them. South Africa continued to strike after the ninth over, taking the last eight Sri Lanka wickets for 45 runs. Hashim Amla then led the chase with an unbeaten 56 from 52 balls. Du Plessis said it was disappointing that his team only put on their most complete performance after they had already been knocked out.

"We've had signs of playing really good cricket through this tournament," he said. "The England game was as good a batting performance as you will see, but obviously not a great bowling performance. Same thing with West Indies - we didn't bat as well as we wanted to, although, on that wicket, 10 more runs would have been par. In both games we did one half of the game really well.

"Tonight, bowling first - as a team that's our strength - the bowlers did really well, and we chased down a small total, which is never easy on these wickets. It was really important for us to have a really good partnership to start off with. That was the only way the team will be in trouble - if they get wickets up front. So after the run-out, it was nice that we could make it a bit stable. It is very bittersweet to be going back to South Africa after the World T20. It was not where we wanted to be. We've only got ourselves to blame."

There is the possibility now that several of their older players may already have played their last World T20 match. Dale Steyn, AB de Villiers and Amla are all 32, and the next World T20 is scheduled for 2020.

"The sad thing is that it's now four years to the next World Cup - it's not just two," du Plessis said. "A few players here won't be there then. That's going to be the challenge now for the squad: to try and rest some of the senior players, to see if they want to go to the next World T20. With that you can breed some young players. There's not a lot of T20 cricket coming up this year, so it will probably take a backseat."

Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @andrewffernando