The bowling unit struggled to take regular wickets whilst they also failed to slow the scoring rate down and despite needing 193 from 24 overs in their adjusted run chase, Sri Lanka couldn't score runs quickly enough as they fell well short in their quest.
De Kock followed up his century in the previous game with 51 from 57 balls as he blasted South Africa to a fast start in pursuit of the win.
Batting at number nine in the order, Udana smashed 78 off only 57 balls to rescue the visitors' innings from 131 for nine.More news: Brazil school shooting: Deadly attack in São Paulo
Anrich Nortje picked up three wickets while Andile Phehlukwayo got two.
Nortje's double-strike only added to Sri Lanka's peril, before small contributions from Kusal Mendis (21) and Dhananjaya de Silva (22), and Udana's impressive hitting helped lift them to a total of sorts.
The 28-year-old did not bat as Sri Lanka slumped to a 71-run Duckworth-Lewis-Stern loss in the third ODI.More news: Fox News' Tucker Carlson Calls Iraqis "Semiliterate Primitive Monkeys" in Surfaced Recording
Hendricks played as an opener in the first three games of the series, all won by South Africa, but managed scores of only 1, 29 and 4, dealing a blow to his chances of making the squad for the World Cup in England and Wales starting in late May.
Captain Faf du Plessis chipped in with 43 and JP Duminy showed form after his return from long-term injury with 31 not out. It was always the intention of the selectors to rotate Hashim and Reeza during this Sri Lanka ODI series'.More news: K-pop star Jung Joon-young quits over sex tape scandal