He first took a brilliant catch leaping high to his right at short mid-on to send back Kusal Mendis and then in the 18th over affected a sensational run-out to dismiss Dinesh Chandimal.
Earlier, the Proteas' total of 299/6 had been built on the back of Hashim Amla's 25th one-day global ton, a brilliant 75 from Faf du Plessis and a quickfire 38 at the end of the innings by JP Duminy.
Niroshan Dickwella (41) and Upul Tharanga (57) started the innings cautiously much like the South African openers, scoring 10 runs off three overs.
South Africa's Morne Morkel made the first breakthrough when he dismissed the risky Niroshan Dickwella for 41 after the Sri Lanka opener's attempted drive down the ground resulted in a comfortable catch for Wayne Parnell at third man.
The Proteas started off to a slow start, with openers Hashim Amla and Quinton de Kock posting 44 runs in 12 overs.More news: Trump slams Qatar for funding terror as Tillerson urges calm
The bowling effort was labelled "ridiculous" by former New Zealand skipper and worldwide coach Stephen Fleming and threatens to further derail the Sri Lankans' tournament following their 96-run defeat by the Proteas. Tharanga - leading in place of the injured Angelo Mathews - hoped there would be some swing in the air, and also expected conditions to get better for batting through the game.
Sri Lanka skipper and all-rounder Angelo Mathews has been forced to sit out during South Africa match, after scans revealed some days ago he´d suffered a calf strain. "Sri Lanka have always done well in ICC tournaments, so we have that confidence", Tharanga said. Skipper AB won't have a tough time in choosing him over the experienced but expensive Imran Tahir. The same over saw leg-spinner Tahir removing Chamara Kapugedera (0) with a lbw decision.
In case you are away from your television, you can watch South Africa vs Sri Lanka live streaming on Hotstar.com. Malinga also failed to take a wicket in his 10 overs but, after all his injuries, he will be relieved to have come through the innings apparently unscathed.
Amla hit 103, his 25th one-day global century, as South Africa posted 299 for six from their 50 overs at the Oval. "He's a great asset for us and it was a fantastic performance".
Sri Lanka will take that last option gladly, because what they need is experience.