Opting to bat first, the Proteas lost two early wickets before de Kock, who made a quick-fire 56 in 33 balls before retiring, and Duminy (67 in 44 balls) feasted well on the Indian offerings on a Wankhede Stadium batting track.
Watched by a huge crowd of over 25,000, India did well in the first four overs by sending back opener Hashim Amla and captain Faf du Plessis with 33 on the board.
At the end of the first six-over power play, the Proteas had hit their way to 67 for two, an excellent start even though they lost two senior batsmen.
Amla edged an attempted drive to Mahendra Singh Dhoni off Bumrah while du Plessis sliced a drive to backward point off Mohammed Shami.
But Duminy, who struck three sixes and six fours, and de Kock carted Bumrah for two fours each in the fifth over. De Kock then struck Harbhajan, in the off-spinner's second over, for a six and a four off the sixth to undo the earlier good work by India.
De Kock showed his ability to play spin bowling with the help of quicksilver footwork to complete his 50 in just 28 balls, inclusive of two sixes and seven hits to the fence, and then retired with the score on 110 for 2.
The two left-handed batsmen put on 77 runs for the third wicket, quite comfortably and at a brisk rate.
Later, Suresh Raina was carted for one six and two fours in the 14th over to give the South African innings an impetus by another left hander, David Miller in his brief stay.
India opted to keep out regulars R Ashwin and Ashish Nehra in their second and last warm-up game.
