Sanju Samson's maiden ODI ton takes India to series win in South Africa
It is the second time India have claimed an ODI series win in South Africa as they posted an above-par 296 for eight in their 50 overs after being surprisingly sent into bat.
South Africa kept up with the run-rate for much of their reply but lost wickets at regular intervals on a pitch not conducive to expansive stroke-play and were bowled out for 218.
That made Samson's effort all the more impressive as he took 66 balls to pass 50 and a further 54 deliveries to reach his maiden international hundred.
"We had to take a bit of extra time to see how the pitch plays and how the bowler is trying to get you out," Samson said.
"Batting higher up gave me those extra 20 balls to assess that. I focussed on my process, there is a lot of hard work that has been done on that recently."
India had been in some early trouble after the early dismissals of debutant opener Rajat Patidar (22) and Sai Sudharsan (10).
But Tilak Varma (52 from 77 balls) and Samson put on 116 for the fourth wicket in the sweltering heat of Paarl, and Rinku Singh contributed a quick-fire 38 from 27 balls at the end of the innings.
South Africa opener Tony de Zorzi blazed a century in the last game and his 81 this time round was the only score of substance in the home side's reply.
Several batters made starts but India's bowlers were disciplined with their lines, and spinner Washington Sundar (2-38) and seamer Arshdeep Singh (4-30) were particularly impressive forcing scoreboard pressure to take wickets.
"We were up for it, it was a series decider at a great venue with a pretty full house (of spectators)," South Africa captain Aiden Markram said.
"Our skills just let us down. We were good in small patches but could not stretch those out long enough to get momentum on our side.
"I don’t think the surface changed much through the day and I thought 290 was chaseable."
Both teams had rested several frontline players ahead of a two-match Test series that starts in Pretoria on Tuesday.