India reached 111 for four at tea after bowling South Africa out for 55 on the opening day of the second and final Test here on Wednesday.
Virat Kohli and KL Rahul were batting on 20 and 0 respectively at the break.
Captain Rohit Sharma and Shubman Gill made 39 and 36 respectively.
India, who had lost the first Test in Centurion, have now taken a first innings lead of 56 runs with six wickets in hand. Earlier, pacer Mohammed Siraj ripped through the South Africa batting line-up with a sensational six-wicket haul as India bowled the home side out for just 55 at lunch.
Captain Dean Elgar's decision to bat first after winning the toss in his farewell Test turned out to be a nightmare for the home side.
Kyle Verreynne made 15 and David Bedingham 12 as all the other remaining South African batters were dismissed for single-digit scores.
Jasprit Bumrah (2/25) and Mukesh Kumar (2/0) took the other South African wickets.
Brief Scores: South Africa: 55 all out in 23.2 overs (Kyle Verreynne 15; Mohammed Siraj 6/15).
India: 111 for 4 in 24 overs (Rohit Sharma 39, Shubman Gill 36; Nandre Burger 3/42).
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