India beat the Proteas by 82 runs in Rajkot on Friday to set up a series decider in Bengaluru on Sunday.
Dinesh Karthik smashed 55 off 27 deliveries to guide India to 169-6, a total their bowlers defended by dismissing South Africa for 87 to level the five-match series at 2-2.
The Proteas slipped to their lowest ever T20I total, two lower than their 89 all out against Australia in Johannesburg in 2020.
Avesh Khan returned his T20I best figures of 4-18 as the hosts defended their total with ease for the second time in a row.
The in-form Karthik set up the crushing victory with his maiden T20I fifty to lift India from a precarious 81-4 in the 13th over to take the attack to the opposition.
He put on a crucial 65-run stand with Hardik Pandya, who hit 46 off 31 deliveries, as the pair hammered the opposition bowlers to all parts of the ground.
The 37-year-old Karthik, who is enjoying his second coming with the national team, smashed nine fours and two sixes as he surpassed his previous best of 48 to make India plunder 73 runs from the final five overs.
Returning fast bowler Lungi Ngidi took two wickets.
In reply, the visitors were never in the chase after skipper Temba Bavuma retired hurt on eight with an injured elbow and the team soon lost two wickets.
Wicketkeeper-batsman Quinton de Kock was run out for 14 and Dwaine Pretorius out to Avesh in the fifth over.
Wickets kept tumbling and Harshal Patel raised the pitch at the nearly packed house after he bowled the dangerous David Miller for nine.
Avesh returned to take three wickets including Rassie van der Dussen for 20 in the 14th over to flatten South Africa on a seemingly tough pitch to bat.
Spinner Axar Patel got the ninth wicket to end the Proteas’ innings in 16.5 overs as Bavuma, who sat in the dugout with an ice pack on his elbow, did not come out back to bat.
© Agence France-Presse