Pakistan, fighting to save the second Test, were struggling at two for two at lunch after South Africa piled up a mammoth 517 on the third day in Dubai today.
After conceding a huge 418-run lead, Pakistan lost both openers, Shan Masood (nought) and Khurram Manzoor for his second duck, in a disastrous start to their second innings.
Steyn removed Masood with a sharp incoming delivery, trapphim lbw, while Manzoor was caught in the slip off Vernon Philander's fifth ball.
Manzoor, who hit 146 in Pakistan's seven-wicket win in the first Test in Abu Dhabi, got a pair.
At the break, Azhar Ali was unbeaten on two after an extended two-and-a-half hour session due to Friday prayers.
That was far from the ideal start Pakistan needed as they were left frustrated by Graeme Smith (234) and AB De Villiers (164) as South Africa took command of the match after bowling Pakistan out for a paltry 99.
South Africa had resumed their first innings on 460-4 but managed to add just 57 as off-spinner Saeed Ajmal warpped up the innings with 6-151.
De Villiers was the first to go as he slashed at an outgoing delivery and was smartly caught by wicket-keeper Adnan Akmal.
De Villiers hit 17 fours and a six during a commanding 376-minute innings and completed an all-time South African fifth wicket record partnership of 338 with Smith.
Irfan could have removed Smith in his next over but Akmal once again faltered behind the stumps, dropping a shoulder-high catch to his left.
But unlike Akmal's dropped catch off De Villiers on the very first ball on Thursday, this didn't prove costly as Smith was caught in the slip by Younis Khan in Ajmal's next over.
Smith's superb knock lasted 10 hours and 32 minutes during which he dominated Pakistan's bowling, hitting 16 boundaries and facing 388 balls.
With that catch, Younis beat Javed Miandad's record of most Test catches of 93. It took him 86 Tests, 38 fewer than his illustrious countryman.
Irfan continued his demolition when he removed Jean-Paul Duminy in his next over with a fuller length delivery for seven.
Pakistan suffered another jolt when Irfan was removed from the bowling attack by Australian umpire Rod Tucker for running into the danger zone after a second warning.
Ajmal removed the tail by dismissing the last three wickets for his ninth five-wicket haul in Tests.
