South Africa veterans Hashim Amla and Faf Du Plessis dented Sri Lanka's hopes of pipping England to a World Cup semi-final spot at Chester-le-Street.
Victory for Sri Lanka would have moved them level on points with the tournament hosts, but they lost wickets at regular intervals, a number of their batsmen bogged down on a slow pitch as they posted 203 all out.
The paltry target provided few problems for Amla (80 not out) and Du Plessis (96no) in a 175-run partnership which carried the Proteas, already eliminated from contention for the knockout stages, to a thumping nine-wicket win.
The duo, with more than 300 one-day international appearances between them, overhauled the total with 12.4 overs to spare, largely eschewing risk but keeping the scoreboard ticking over, contrasting sharply with Sri Lanka's batsmen.
Eight of Sri Lanka's top nine reached double figures but no one went beyond 30, while a number endured painstaking displays at the crease, Dwaine Pretorius' three for 25 the most economical 10-over analysis of the tournament.
Not even a swarm of bees that swept across the ground towards the end of their innings could sting them into action, while the yellow jersey they had worn in their shock win over England and which they were given dispensation to wear brought them no joy this time.
They were up against it from ball one. Kagiso Rabada immediately vindicated South Africa captain Du Plessis' decision to field first as Dimuth Karunaratne was out first ball, unable to lower his hands to a lifting delivery and sending a looping catch to second slip.
Avishka Fernando displayed similar carefree abandon as he had in the shock win over England last week, interspersing glorious strokes with looser ones in a healthy 67-run stand with Kusal Perera.
However, seeking to stay on the front foot, Fernando, on 30, holed out to mid-off from the penultimate delivery of the first powerplay off Pretorius, who had his second wicket in his next over when Perera chopped on, also for 30.
The pair's dismissals marked an extended period of stagnation for Sri Lanka, whose innings never quite recovered its momentum, Kusal Mendis and Angelo Mathews progressing at a snail's pace more akin to a Test match.
Only 24 runs were added in the 10 overs after the first powerplay, after which Mathews attempted to release some pressure only to bottom edge Chris Morris on to his stumps for 11 off 29 balls.
Mendis' ponderous 23 from 51 balls was ended when he slapped to Pretorius at cover, leaving Sri Lanka on 111 for five as Dhananjaya De Silva and Jeevan Mendis attempted to redress the balance, ultimately in vain.
The pair were circumspect to a fault before losing their wickets while looking to accelerate, De Silva bowled after missing a reverse sweep to JP Duminy's first ball and Mendis holing out to long leg off Morris.
Between the start of the 11th over and the end of the 40th, Sri Lanka had added only 96 runs before the bees came, forcing players and umpires alike to take evasive action, lying flat on the floor.
It was a momentary distraction before Sri Lanka were all out with three balls of their innings unused.
South Africa's reply started with Amla cover driving and then flicking off his legs for back-to-back fours off Lasith Malinga, who then castled Quinton De Kock for 16 with a superb dipping yorker.
But Amla's timing and Du Plessis' vigour and occasional forcefulness ensured South Africa would not go into their shells as Sri Lanka had done earlier.
The experienced pair still had to be watchful, but Amla was relatively untroubled in a 55-ball half-century and the union between himself and Du Plessis stretched into three figures not long afterwards.
Du Plessis reached 50 after 70 balls before powering Suranga Lakmal for a straight six, while Amla successfully reviewed an lbw decision off Jeevan Mendis on 68.
Amla had started walking off the pitch, only for technology to show the ball had pitched outside leg stump, but after being called back he and Du Plessis ushered South Africa serenely to a consolation victory.
