Rohit Sharma inspired India to a victory over South Africa and a series win that ensures they will leapfrog the Proteas and go top of the one-day rankings.
India had already clinched at least a share of the six-match series as they went into the penultimate ODI in Port Elizabeth holding a 3-1 lead, and they duly continued their dominance in a 73-run win.
Having been put into bat India owed a debt of gratitude to Rohit for pushing them to 274-7 with 115 off 126.
Hashim Amla (71) and Heinrich Klaasen (39) gave the Proteas hope, but the run out of the former proved a key moment in the game and when Klaasen fell to the excellent Kuldeep Yadav the writing was on the wall.
India will now look to finish with a flourish in the series finale in Centurion on Friday.
BREAKING: India will finish the #SAvIND ODI series as the number one side in the @MRFWorldwide ICC ODI Rankings after taking a 4-1 series lead with victory in Port Elizabeth!https://t.co/1oA76LNlyI pic.twitter.com/xNpiqW6kFC— ICC (@ICC) February 13, 2018
Shikhar Dhawan got India's innings off to a quick start as he struck 34 off 23 balls in his opening partnership of 48 with Rohit, striking eight fours before he pulled Kagiso Rabada to deep square leg.
Rohit duly picked up where Dhawan had left off, contributing 62 off only 55 deliveries in a second-wicket stand of 105 with Virat Kohli, who was on 36 when he was run out by JP Duminy.
Kohli's dismissal came as a result of Rohit refusing to run and Ajinkya Rahane (8) went in similar fashion as India's centurion was caught ball-watching.
But Rohit, dropped on 96 by Tabraiz Shamsi, made up for those mental errors as he brought up his first hundred in South Africa with a flick past backward square leg.
Rohit eventually fell to Lundi Ngidi (4-51), who had Hardik Pandya for a duck next ball, but Bhuvneshwar Kumar (19 off 20) helped push India to a total that proved well beyond South Africa.
Aiden Markram went for a run-a-ball 32 as he combined for 52 opening runs with Amla, who found little in the way of support as Duminy (1) and AB de Villiers (6) both failed.
Amla, who hit just five boundaries in a workmanlike 92-ball stay, looked to have found a match-winning partner in Klaasen, but an extremely tight direct hit run out review went against him and sparked a Proteas collapse.
Kuldeep then removed Andile Phehlukwayo and Rabada and all hope went when the same bowler had Klaasen stumped as India dethroned South Africa as the top team in the 50-over game.