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.
Experienced pair Faf Du Plessis and Hashim Amla guided South Africa past Sri Lanka
Du Plessis gestures at Amla, who had walked off despite being given a DRS reprieve
Amla hit 80 not out as the Proteas eased to their second win of the Cricket World Cup
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.
Kagiso Rabada celebrates after dismissing Dimuth Karunaratne with the first ball of the match
Avishka Fernando displayed similar carefree abandon as he had in the shock win over England last week, interspersing
