Delhi - India strengthened their position despite two early strikes by South Africa paceman Morne Morkel on the third day of the fourth and final Test in New Delhi on Saturday.
At lunch, the hosts were 51-2 for a lead of 264 runs with eight wickets in hand.
Shikhar Dhawan (20) and Cheteshwar Pujara (27) were the unbeaten batsmen at the crease.
India, who have already sealed the series with wins in the first and third Tests, had bowled out the top-ranked tourists for 121 after making 334 for a first-innings lead of 213 runs.
The Indians were off to a shaky start in their second knock, losing two wickets with just eight runs on the board.
Opener Murali Vijay was out to a rising ball from Morkel that appeared to have grazed his armguard before flying through to wicketkeeper Dane Vilas, who leapt high in the air to take a one-handed catch over his head.
Vijay looked displeased with the decision, shaking his head as he walked off the ground.
Morkel struck again with the first ball of his next over to dismiss the struggling Rohit Sharma for a golden duck, the ball zipping past his bat and flattening the off-stump.
Sharma's best score in the series has been a 23 in Nagpur, raising doubts about his temperament in the longest form of the game.
Pujara appeared confident at the crease, once hitting two fours in an over from fast bowler Kyle Abbott.
Dhawan, celebrating his 30th birthday Saturday, was more careful in his approach, taking 72 deliveries to score 20.
With the track at the Feroz Shah Kotla ground looking good for batting, India will hope to pile on the runs before setting a target for the struggling Proteas who have been dismissed for less than 200 in five of the six innings in the ongoing series.