There was a bit of a buzz for a while, but it didn't last long. A swarm of bees halted the game in the 48th over. All the players and both umpires went to ground, face down, to avoid any stings before play continued and Sri Lanka was quickly dismissed for 203.
South Africa lost only one wicket — Quinton de Kock (15) bowled by a trademark Lasith Malinga yorker — in coasting to victory with more than 12 overs to spare.
Skipper Faf du Plessis scored 96 and Hashim Amla 80 in an unbeaten 175-run stand, easily South Africa's best of the tournament.
Du Plessis posted his third half-century of the tournament with a single from Suranga Lakmal, then drove the next delivery over temporary broadcasting scaffolding and out of the ground, requiring a used replacement ball for the rest of the match.
Amla was on 68 when was given out lbw to Jeevan Mendis with the total at 166-1 and had just about left the field when the referral to the TV umpire showed the ball pitched outside leg stump and he had to make his way back to the crease.
The South Africans were already out of semifinal contention after winning just one of their first seven games, but had won 16 of their previous 18 ODIs against Sri Lanka and got on top quickly.
Sri Lanka was coming off an upset win over England that changed the momentum of the tournament, exposing the hosts to the possibility of missing out on the playoffs.
Another win would have moved Sri Lanka past Bangladesh and Pakistan to equal on eight points with fourth-placed England, but the bowlers were unable this time to defend a small total.
Malinga, who took four wickets last week as Sri Lanka defended 232-9 in the 20-run win over England, didn't get the same kind of traction in warm, sunny conditions in the first game of the tournament in Durham.
South Africa's bowlers were more impressive by contrast, preventing any Sri Lanka batsman from scoring more than 30.
Paceman Kagiso Rabada (2-36) removed Dimuth Karunaratne with a well-directed short ball that the Sri Lanka skipper could only fend away to du Plessis at second slip. That made Karunaratne just the second batsman dismissed on the first ball of a match in this tournament.
Sri Lanka recovered through a 67-run partnership between second-wicket pair Avishka Fernando and Kusal Perera, who both scored 30, before recalled allrounder Dwaine Pretorius dismissed them in the 10th and 12th overs.
Chris Morris (3-46) picked up the key wicket of Angelo Mathews, who scored an unbeaten 85 against England, when the allrounder was on 11 and dragged an attempted pull shot onto his stumps.
Pretorius, playing his first game since conceding 42 in seven overs and scoring 1 in South Africa's opening loss to England, then dismissed Kusal Mendis (23) to return 3-25 from 10 overs, the most economical bowling figures so far at the tournament.
Sri Lanka can still reach the semis, but needs to win remaining group games against West Indies and India and rely on other results going its way.