Steyn destroyed India with a fierce spell in which he claimed a career-best seven for 51, bowling India out for a measly 233 and handing South Africa a first-innings lead of 325, with India, who were forced to follow on, 66-2 at stumps.
India were fairly well placed at 221 for four at the tea interval, but Steyn returned to pick up five wickets in 3.4 overs after the interval as India caved in meekly.
"We actually had the ball changed when we came out after tea because the seam had popped open on the old one," Steyn said.
"We hoped to get a bit of reverse swing.
"It worked in our favour and it was good really."
India were still 259 behind at close and will need an inspired performance just to force South Africa to bat again.