Openers de Kock and Hendricks made unbeaten half-centuries in a comprehensive 10-wicket win.
Comprehensive South Africa clinch T20I series against Sri Lanka, to take an unassailable 2-0 lead in the series.
Even five dropped catches from South Africa could not take the hosts over the line.
Chasing 204, South Africa were bundled out for 125 as the Sri Lanka spinners weaved their magic in the third and final ODI in Colombo.
Despite Charith Asalanka career-best 77, Sri Lanka were never really able to keep up with the required scoring rate.
Sri Lanka bowl brilliantly at death to restrict South Africa to 286/6 and win the first ODI by 14 runs
Dinesh Chandimal also returns as Sri Lanka announce squad for South Africa series
The teams had also faced off earlier in the year when Sri Lanka played two Tests in South Africa.
