The Proteas were bundled out for just 126 in the first innings of the first Test in Galle, before crumbling to 73 all out in their second knock to slump to a demoralising 278-run defeat inside three days.
Du Plessis pinpointed South Africa’s failure to build on a promising start with the ball when it had Sri Lanka five down for 119 runs as the turning point of the match.
“We’ve only got ourselves to blame for that situation,” he said. “That [conceding the lead] was a big turning point in the game.
“You bat first on a wicket that was never going to be a high-scoring pitch – I think we had them at 115-5, and we let them to get to 287.
“Obviously, it was a big total. Even though we bowled well in the second innings, that was always going to be a difficult total.”
Only three players made it into double figures in South Africa’s second innings, while Sri Lanka’s spin duo of Dilruwan Perera and Rangana Herath claimed 15 wickets between them in a one-sided contest.
Asked about the team’s preparation for spin, Du Plessis added: “Leading up to a series like this, the quality that you’re going to get from some of the spinners, it’s not something you can just practice against in the nets.
“The quality of spin in this Test match and how they controlled it was fantastic. So that’s where we’ve to improve, especially in these conditions where you’ve to make a play.
“That’s what we’ll look into ahead of the next Test match.”
Sri Lanka’s stand-in skipper Suranga Lakmal, who has won both his assignments as captain in the absence of the banned Dinesh Chandimal, hailed Perera and Herath among the best spinners in the world.
“Rangana is one of the leading left-arm spinners in the world. No questions on that front,” he said.
“Dilruwan too has been bowling pretty well during the last couple of years. Both of them are leading spinners in the world at the moment.
“Especially in Galle, they have won matches for us. I hope they will continue the good work they have been doing.
“South Africa is the number two team in the world and we are at the sixth place.
“When we play against such a formidable team, we can never have expectations like this [winning this easily] but as we go on, we may have an idea.”