Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @afidelf
South Africa 190 for 4 (De Kock 51, du Plessis 43, Duminy 31*, Dhananjaya 3-41) beat Sri Lanka 189 all out (Udana 78, Nortje 3-57, Phehlukwayo 2-21) by 6 wickets
South Africa made four changes to their XI, and Sri Lanka swapped three of their players out, but no matter how much the hosts experiment, and how desperately the visitors try to scramble together a better side, a comfortable victory for South Africa almost seems inevitable at this point.
This one was the most embarrassing result for Sri Lanka yet. They collapsed, more or less non-stop, from the third to 34th over, losing their ninth wicket with only 131 on the board. No. 9 Isuru Udana added a measure of respectability to the total with an adventurous 78 off 57 balls, but still, a total of 189 was all they could manage.
South Africa were never going to be daunted by that target, particularly on a track that was only slightly two-paced, rather than being a minefield. They lost Reeza Hendricks early again, but Quinton de Kock got his usual solid start and made his fifth consecutive 50-plus score in ODIs, before Faf du Plessis chipped in with a rapid 43, and the middle order finished the job. The winning run was hit in the 33rd over, with six wickets in hand.
South Africa will be pleased with how some of their World Cup hopefuls have performed in this series, but might now be wishing they had had a tougher opposition to test themselves against in the approach to the global event.
For what it is worth, though, South Africa's bowlers prospered today - Anrich Nortje picking up figures of 3 for 57, his wickets largely the result of the extra bounce he was able to generate. Andile Phehlukwayo was the most disciplined on show, taking 2 for 21, while Dale Steyn, Lungi Ngidi, Tabraiz Shamsi and even JP Duminy picked up a wicket apiece. None of these bowlers were particularly menacing but they bowled tightly, and only had to await the opposition mistakes.
Sri Lanka's innings began poorly, with Upul Tharanga and Oshada Fernando losing their wickets to Steyn and Ngidi respectively nside the first four overs, before Kusal Mendis and Avishka Fernando attempted a recovery. The pair seemed to have the measure of the South Africa bowlers by the end of the Powerplay, but as has often been the case with this Sri Lanka team, the partnership was broken before it could truly mature - Avishka jabbing Nortje to short midwicket for 29, in the 11th over.
From there the wickets came frequently. Debutant Priyamal Perera was out first ball, gloving Nortje down the legside. Kamindu Mendis was also caught behind, nicking an attempted cut off Nortje. There was no significant partnership until the last-wicket stand. Kusal Mendis was out for 21 trying to pull Phehlukwayo. Thisara Perera chipped a Tabraiz Shamsi ball back Shamsi, who took a good catch diving forward. Captain Lasith Malinga's dismissal, though, was perhaps the most reprehensible of all. Calling Udana through for a single towards midwicket, Malinga ambled the run, did not slide his bat, and was caught short by the direct hit by Reeza Hendricks. When he left, Sri Lanka were 131 for 9.
So far back were Sri Lanka by this stage, tha Udana's heroics would not ultimately matter, but they were laudable nonetheless. He struck three sixes - in the arc between midwicket and long on - and multiple fours through cover and long off. At a time when South Africa were perhaps guilty of easing back on the intensity, Udana repeatedly found the boundary, forging a 58-run stand with No. 11 Kasun Rajitha, who held doggedly on to his wicket, but did not contribute a single run.
Even Udana's best List A score could not lift Sri Lanka to a competitive total however, and despite losing Hendricks in the fifth over to the offspin of Dhananjaya de Silva, South Africa always seemed to have the measure of their target. By the time the Powerplay was done, the hosts had set a base, with 45 for 1 on the board. Aiden Markram could not transfer his outstanding form from domestic one-day cricket into the international arena, eventually getting out for 29 to Kasun Rajitha, but de Kock, and later du Plessis, continued South Africa's brisk advance.
The offspin of de Silva claimed three South Africa wickets for 41 runs, but even those good returns could not make a serious dent in the hosts' chase. JP Duminy took them home in style, hitting a six and four fours in a 31 not out that came off 21 deliveries.