Mark Boucher won his first Test series as South Africa coach as the Proteas thrashed England's next opponents Sri Lanka within three days in the second Test.
That left South Africa needing just 67 to win and Dean Elgar and Aiden Markram wrapped up the 10-wicket win in just 13.2 overs.
Sri Lanka's two-Test series against England starts on 14 January.
Former wicketkeeper-batsman Boucher took over as South Africa head coach in December 2019 and lost his only previous Test series against England 3-1.
Sri Lanka, who were ranked fifth in the world - above South Africa - before the series, have suffered two heavy defeats on this tour after losing the first Test by an innings and 45 runs in Centurion last week.
They started day three with a slender five-run lead, and Karunaratne and wicketkeeper Niroshan Dickwella added 26 before the former was dismissed by Anrich Nortje's short ball.
Dickwella fell to the impressive Ngidi four balls later before pace bowler Lutho Sipamla, in just his second Test, took three wickets to wrap up the tail.
Markram and Elgar - who made a century in the first innings - made light work of the required target to seal a convincing Test and series win.