Fernando made 75 not out off 106 balls and Mendis scored 84 not out off 110 deliveries as Sri Lanka chased down a victory target of 197, reaching the mark by lunch. Resuming at 60 for two, Fernando and Mendis batted positively from the start of play, scoring nine runs off the second over of the day, bowled by Kagiso Rabada.
No South African bowler was able to settle into a consistent rhythm.Dale Steyn was brought into the attack after 36 runs had been scored off the first eight overs of the morning. Mendis struck three boundaries in the first over from South Africa's all-time leading wicket-taker.
Left-arm spinner Keshav Maharaj extracted some sharp turn from a pitch which otherwise offered nothing to the bowlers despite the extraordinary events of the first two days when 31 wickets fell.
But the batsmen used their feet against Maharaj who conceded 23 runs off four overs, including a straight six by Fernando, before being taken off. Mendis was dropped on 70 when a leaping Hashim Amla at first slip could only get his fingertips to a slash against Duanne Olivier. By then, though, only 31 runs were needed.
Sri Lanka's series win was one of the biggest upsets in recent cricket history.South Africa had won their previous seven series at home and had won 16 out of 19 home Tests, with only two defeats, before losing in Durban.
Sri Lanka, by contrast, had lost six and drawn one of their previous seven Tests before arriving in South Africa with their team seemingly in disarray.
The selectors had made wholesale changes, including the dropping of captain Dinesh Chandimal, several players were missing because of injuries, while coach Chandika Hathurusingha was stripped of some of his powers. Yet the Sri Lankans heeded the call of Dimuth Karunaratne, who was announced as 'interim' captain, to “compete in every session” and to play with a smile on their faces.
The win in the second Test was set up by the Sri Lankan bowlers after South Africa led by 68 runs on the first innings. Despite the absence of injured left-arm spinner Lasith Embuldeniya, South Africa were bowled out for 138, leaving Sri Lanka with a target which Fernando and Mendis made to appear easy.
South Africa, first innings, 222
Sri Lanka, first innings, 154
South Africa, second innings, 128
Sri Lanka, second innings (overnight 60-2)
D. Karunaratne c De Kock b Olivier19
L. Thirimanne c De Kock b Rabada10
O. Fernando not out75
K. Mendis not out84
Extras (b4, lb5)9
Total (2 wkts, 45.4 overs)197
Fall of wickets: 1-32 (Thirimanne), 2-34 (Karunaratne) Bowling: Steyn 8-0-38-0, Rabada 15-2-53-1, Olivier 12-2-46-1, Mulder 4-1-6-0, Maharaj 6.4-0-45-0 Match situation:
