Pathan made full use of the two lives to smash the fastest fifty in IPL history as KKR knocked off a 161-run target in 14.2 overs when they were required to overhaul it in 15.2 to make it to top-two.
Pathan enthralled the packed Eden Gardens crowd with his exceptional knock which featured seven sixes and five fours.
After being dropped on nought and 15, he completed his half-century in just 15 balls.
The result pushed Chennai Super Kings to third place and KKR will now clash with table toppers Kings XI Punjab in the first Qualifier on May 27 at Eden Gardens.
Leading run-getter Robin Uthappa (41) and Gautam Gambhir (28) set up the chase before Yusuf's blitz.
Yusuf was on his way back to dug out before he could open his account after hitting straight to midwicket fielder Anirudha, who dropped the sitter.
It would have been a second wicket in the Karn Sharma's over after the leggie dismissed Manish Pandey but the breather turned around KKR's fortunes as they were reeling 78/4 in 9.4 overs after Uthappa (41) and Ten Doeschate were dismissed in the same over.
Yusuf made his intention clear in the next over when he slammed Parvez Rasool one six and a boundary and even got a second life when Steyn dropped him at the square leg boundary, that went over the rope. The JK spinner leaked 22 runs in that over.
Steyn had to bear the brunt of dropping Yusuf as the biggest onslaught from the Baroda hitter came only against the South African speedster who conceded 26 runs in his last over with two sixes and three fours.
Such was Yusuf's fury that he made the world's no 1 bowler look sorry with the bowling sequence of 4-6-6-4-4-2.
SRH skipper Darren Sammy (29) had guided Sunrisers to a 160 for seven after being invited to bat. Shikhar Dhawan (29 from 31 balls) and Naman Ojha (26 from 23 balls) also contributed in team's total.