He and captain AB de Villiers (109 from 101 balls) catapulted South Africa to 301 for eight in their 50 overs, boosted by a fine cameo from David Miller who made 56 not out from 34 balls.
De Kock joined Pakistanis Zaheer Abbas and Saeed Anwar as well as compatriots Herschelle Gibbs and De Villiers as the only men to have scored hundreds in three consecutive one-day internationals.
Ishant Sharma was the best of the Indian bowlers with figures of four for 40 in 10 overs.
The rain arrived at the change of innings, though, and the umpires called off play without a ball being bowled in the Indian reply.
South Africa had already claimed the three-match series after winning the first two matches in Johannesburg and Durban.
The teams will now switch focus to a two-match test series starting at The Wanderers in Johannesburg on December 18.
(Reporting by Nick Said in Cape Town; editing by Ed Osmond)
