South Africa now have an unbeatable 2-0 lead in the five-match series. The first game was washed out and South Africa won the second last Wednesday by a massive 157 runs.
Kemp's 100 not out was the top score as South Africa rallied from 76 for six to a total of 274 for seven. Pollock took four for 26 to help dismiss India for 168 in 41.3 overs.
South Africa's recovery began with a stand of 60 for the seventh wicket between Kemp and Pollock.
The 138 runs that Kemp and Andrew Hall, who scored 56, shared in an unbroken stand was a world record for the eighth wicket in one-dayers. The runs flowed at a rate of 9.74 an over.
''We were in trouble after 20 overs, but the boys showed character. Kemp, Pollock and Hall were fantastic. None of us dreamt that they would get us to 274,'' South African captain Graeme Smith told reporters.
''I think the coach (Mickey Arthur) had a quiet prayer for 180,'' he added.
The previous eighth wicket record was the 119 runs that Shane Warne and Paul Reiffel put on for Australia against South Africa in Port Elizabeth in 1993-94.
Scorecard of 3rd ODI
India never recovered from a poor start, losing their first wicket before they had scored a run when Virender Sehwag attempted to cut Pollock's fourth ball of the innings and sent a top edge looping to third man.
Pollock struck again in the fifth over when Sachin Tendulkar pulled at a short delivery and was comfortably caught by Loots Bosman at square leg for two.
India were reduced to 17 for three in the ninth over when Pollock bowled Mohammad Kaif off the edge of his bat for 10, and the visitors were 44 for four when Dinesh Karthik edged Makhaya Ntini to Smith at second slip to go for 14.
Captain Rahul Dravid's 63, which he scored off 103 balls with four fours and a six, was the best of India's batting.
The loss left Dravid searching for positives ahead of the fourth game of the series in Port Elizabeth on Wednesday.
''We must remember that we had South Africa in trouble early on in both the games that we've played, and that's a good positive for us,'' Dravid said.
''We've got some batsmen scoring runs, but we need more contributions with the bat.''