India fought back superbly on day one of the third and final Test in Kanpur to bowl South Africa out for 265.
Graeme Smith (69) and Hashim Amla led the Proteas to 152-1 after tea, before India's spinners and paceman Ishant Sharma (3-55) took control.
Spin pair Harbhajan Singh and Piyush Chawla, 19, shared five wickets.
India, skippered by Mahendra Dhoni in the absence of the injured Anil Kumble, need to win the game to level the three-match series.
If they do, it will be without captain Kumble, who failed a morning fitness test on his injured groin and must sit out the decisive encounter.
The Proteas made an impressive start in Kanpur, knowing a draw in the Test would be enough to move them up to number two behind Australia in the ICC's Test rankings.
Captain Smith and fellow opener Neil McKenzie shared a stand of 61 before McKenzie danced down the track to Chawla and was stumped by Dhoni.
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Leg-spinner Chawla, playing his first Test for two years and ably supporting the more experienced Harbhajan, was expensive but he was getting the ball to turn on a pitch that was already beginning to crack up.
Smith and Amla took the score on to 152 after lunch and they seemed in control, the captain reaching his fifty with a six off Chawla.
But he fell for 61, caught off his gloves by short-leg Wasim Jaffer off the recalled Yuvraj Singh, before Amla was cleaned up by Ishant Sharma soon after reaching his half century.
When Harbhajan found a way through Jacques Kallis's defences for just one, the South Africans were in trouble on 161-4.
With Ashwell Prince getting bogged down at one end, AB de Villiers tried to up the tempo, but after reaching 25 he spooned Chawla up in the air and was caught by Sourav Ganguly.
Prince, having laboured to 16 from 71 balls, was finally trapped lbw by the part-time off-spin of Virender Sehwag as India's spinners continued to work their magic.
Morne Morkel and Dale Steyn both succumbed to Harbhajan and Sharma cleaned up Mark Boucher and Paul Harris as the South Africans were bundled out just before close.
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