The effects of the concussion kept Coulter-Nile out of Kolkata's next three matches - with Knight Riders assistant coach Simon Katich telling Indian media on May 6 that the 29-year-old was "off-colour" and would not be rushed back - before the paceman returned as a last-minute inclusion for the must-win game against the Sunrisers.
Yusuf Pathan, promoted up the order to score at a brisk pace, lasted just one delivery before he was run out.
The victor of of the match will face the loser of Qualifier 1 between Mumbai Indians and Rising Pune Supergiant on May 19 in Qualifier 2, which will decide the second participant of the final on May 21.
A mighty pulled six from Nathan Coulter-Nile off Mitchell Johnson took the score into three figures amid the flurry of wickets - the maximum proving nothing more than minor irritation for the bowler, who gained his revenge two deliveries later. KKR waited on tenterhooks for the rain to relent and when it finally did, well past midnight, they were left with a target of 48 runs in six overs.
In his next over, Karn dismissed Gambhir and Colin de Grandhomme to leave KKR on the ropes at 31 for 5 after seven overs.
Suryakumar Yadav (31) and Jaggi put a semblance of a fight with a 56-run association for the sixth wicket but could not script a turnaround as the former fell in the 18th over looking to accelerate.
But, once Jaggi was removed by Karn for 28, the collapse continued.
In the end, Mother Nature took pity on KKR. An injury to Krunal then provided the opening for Karn, who also takes the ball away from right-hand batsmen.
After the match, Karn Sharam looked confident of Mumbai's chances of lifting the trophy.
Coulter-Nile grabbed three wickets in four balls to finish with 3-20 from his four overs, including a remarkable caught and bowled to dismiss Chris Jordan.
KKR, who lost four out of seven matches in the latter half of the season, will have to play out of their skins to make it to the second qualifier. The main motivation is when I get a game I need to perform for the team. "The way they hung in there, the kind of batting line-up that Sunrisers have, they had to dig deep", he said.
They face Rising Pune Supergiant in the final in Hyderabad at 15:30 BST on Sunday.
"I was just really exhausted, headaches, I got a bit sick but there wasn't rehab or anything like that, I just had to lay in bed and wait to get right".
With 10 victories in the league stage, table-toppers MI have been in rampaging form and they would like to forget their defeat against Pune and rise to the big occasion.
Mumbai's batting has been their mainstay this season with openers Lendl Simmons and Parthiv Patel giving the team good starts and skipper Rohit Sharma, Ambati Rayadu and Kieron Pollard firing in unison.
On what he does when he is not regularly in the playing eleven, he said, "It's good for me". Karn doesn't think Mumbai are at a disadvantage, though. If the top six batsmen go hard and one of them comes off then you win the game.
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