Vishwa Fernando picked 4 for 62. AFP

Sri Lanka's bowling performance on the opening day in Durban wasn't as surprising as the relentlessness of it. There were glimpses of what the bowling unit can do in Canberra, when they had Australia down at 28 for 3 before conceding a 308-run partnership, and they could bring it all together in Durban, which witnessed South Africa being shot out for 235 on a helpful pitch.

And the reason South Africa could get to 235 from 89 for 4 was in part because of a rattling 94-ball 80 from Quinton de Kock, who confessed to South Africa being caught off-guard by Sri Lanka's less familiar seamers.

"I think they caught us off guard," de Kock said. "Going forward we'll be much more alert to the bowling up front. We've understood that Suranga Lakmal is a serious opening bowler that we have seen a lot of, and have good plans for, but were a bit unaware of the new guys."

At the heart of Sri Lanka's bowling performance were Vishwa Fernando and Kasun Rajitha, who have a sum total of nine Test matches between them. While Fernando picked four in this match, including wickets of Hashim Amla and Aiden Markram, Rajitha provided the breakthroughs in the middle overs, when a partnership so often lets South Africa get away even in tough bowling conditions.

"The two new guys - we hadn't seen much," de Kock said. "We've only played one of them [Rajitha] in white-ball cricket once. The rest, it was unseen before. To understand and change our game plan can be quite tough, especially with the pitch. They bowled really well - they didn't miss their lengths often. We had work hard to get what we did.

"I think what surprised us was just the angle of their bowling and the skills they had. They had different actions, some skiddiness, and some bounce. But with those new guys, the batsmen have had a feel of them now, and we'll come back and see how we are going to go about it. They are two solid bowlers and they will keep us in trouble through the series. We've got to keep our eyes open for them."

Sri Lanka ended the day at 49 for 1 but de Kock is hopeful of South Africa picking wickets early on the second day. "I think early on, in the first hour or two, there definitely will be some movement in the wicket. But I think as the day goes on, it will get better. I also think Keshav Maharaj will come into play a little bit more. As you see, the wicket is spinning quite a bit."