Amir came back into the attack in the 16th over to finish off a jaw-dropping encounter for the Karachi Kings to qualify for the third playoff.
The defending champions Islamabad United have been eliminated after failing to achieve a meagre target of 127 runs, falling short by 44.
Amir, Mir and Imad took three wickets each for the winners on a pitch which favoured bowlers.
Islamabad United 82/9 (15.0): One more wicket will give Karachi Kings a historical victory.
(14.4) OUT! Sohail Khan gets the better of Amad with a slower one to castle him.
Islamabad United 77/8 (14.0): Karachi Kings come closer to victory.
(13.4) OUT! Mir on a hattrick. Sami has been trapped lbw as he tries to play a forward defensive stroke. Islamabad are eight down!
(13.3) OUT! Usama Mir sends United’s last specialist batsman back to the pavilion. The right-hander played it into the hands of Sangakkara in an attempt play a late cut.
Islamabad United 74/6 (13.0): Imad concedes just four as Islamabad United struggle to find the boundary.
(12.1) OUT! Pooran comes in and goes out lbw trying to pull a low-bounce half tracker by Imad Wasim.
Islamabad United 70/5 (12.0): Karachi Kings are on top as United wickets keep falling
(11.5) OUT! Usama Mir sends Shadab Khan back to the pavilion.
Islamabad United 61/4 (11.0): Imad Wasim finishes off the over by clean-bowling United danger-man Shane Watson.
Islamabad United 56/3 (10.0): United, like Karachi in their first innings, have failed to find fluidity as they’re half way through their run chase.
Islamabad United 49/3 (9.0): Imad keeps the defending champions quiet.
(8.1) OUT! Imad castles Misbah.
Islamabad United 47/2 (8.0): Pollard drops Misbah at long-on after Usama Mir is introduced in the attack.
Islamabad United 42/2 (7.0): Imad starts his spell decently.
Islamabad United 34/2 (6.0): Asif Ali pulls Sohail for a maximum and follows it by straight drive for four. Expensive over for the Kings.
Islamabad United 22/2 (5.0): Usman concedes just six as United struggle to find the fence.
Islamabad United 16/2 (4.0): Sohail Khan continues from where Amir stopped, another quiet over for United.
Islamabad United 12/2 (3.0): An over dominated by Amir’s high-octane show puts Islamabad United under pressure.
OUT! Amir strikes again! Brad Haddin has played it on.
OUT! Kumar Sangakkara has pulled of a blinder, the legendary Lankan takes an unbelievable catch behind the wickets as Amir dismisses Smith
Islamabad United 10/0 (2.0): Usman Khan starts off by conceding a four but makes a good come back to concede just one run in the remaining five balls.
Islamabad United 5/0 (1.0): Asif Ali with a smashing cover-drive to start off the chase.
United are out to bat, Mohammad Amir with the new ball.
Islamabad United need 127 runs to win.
OUT! Sami castles Usman Khan to end Karachi’s innings.
OUT! Sami strikes, Usama Mir departs
Karachi Kings 125/8 (19.0): Rumman Raees has delivered a major blow to Karachi’s hopes to clinch the PSL title.
OUT! Rumman is on fire, clean bowls Sohail Khan with a yorker.
OUT! Rumman on a hattrick, gets Pollard this time.
OUT! Imad departs
Karachi Kings 122/5 (18.0): Sami with an economical over.
Karachi Kings 114/5 (17.0): Imad Wasim comes in, scores a six, but Rumman replies back with five good bowls, conceding just two more runs.
Karachi Kings 106/5 (16.0): Kings not scoring as fast as they would like, but they’re keeping the scoreboard ticking.
OUT! Malik run out courtesy a bullet throw by Asif Ali.
in-form Kieron Pollard has come in to bat for the Karachi Kings.
OUT! Bopara departs in an attempt to clear long-on on Watson’s delivery, young Shadab dives to grab a very well-judged catch.
Karachi Kings 100/3 (15.0): Not a very productive over for the Kings.
Karachi Kings 92/3 (14.0): Bopara puts an to Watson’s over with a drive straight down the ground.
Karachi Kings 83/3 (13.0): Shadab signs off with another great over as Bopara escapes dismissal courtesy DRS.
Karachi Kings 81/3 (12.0): Ravi Bopara announces his arrival with a four across the square-leg boundary.
OUT! Sangakkara departs as the left-hander pulls a smart bouncer by Watson right into the hands of the fielder on the legside.
Karachi Kings 74/2 (11.0): Shadab with another good over.
Karachi Kings 66/2 (10.0): Sangakkara ends the over with a beautifully timed flick as Kings fight back.
Misbah hands the ball to Shane Watson.
Karachi Kings 57/2 (9.0): Malik and Sangakkara score a boundary each to ease the pressure after Babar and Gayle’s departure.
Karachi Kings 48/2 (8.0): Karachi Kings finding it hard to score runs as Irfan finishes another disciplined over.
Karachi Kings 45/2 (7.0): Shadab has put the Kings under immense pressure with his hard-to-guess legspin.
Shoaib Malik is on the crease.
OUT! The Kings are in trouble, Shadab traps Babar lbw on the very first ball of his over.
Karachi Kings 41/1 (6.0): Rumman strikes for United just when Karachi looked on course for a big score.
Kings’ skipper Sangakkara comes out to bat.
OUT! Gayle is castled by Rumman’s gun-barrel-straight yorker just after the southpaw launched a towering six into the stands behind square-leg boundary.
Karachi Kings 35/0 (5.0): Gayle finds his touch as the West Indies big-man plunders Sami for two boundaries.
Sami back in the attack.
Karachi Kings 25/0 (4.0): Babar scores another four as Kings stabilise innings.
Early bowling change for United, Rumman replaces Sami for the fourth over.
Karachi Kings 18/0 (3.0): Babar covers up for the loss in the first two overs, smashes Irfan for four classically executed boundaries.
Karachi Kings 0/0 (2.0): Gayle and Babar, worryingly for the Kings, have failed to score in 12 balls, Sami with a well-bowled over.
Karachi Kings 0/0 (1.0): Mohammad Irfan starts off with a maiden courtesy top-notch accuracy.
Chris Gayle and Babar Azam come out to open for Karachi Kings.
Karachi Kings: Babar, Gayle, Sangakkara, Malik, Pollard, Bopara, Imad, Sohail, Amir, Usama, Usman
Islamabad United: Smith, Pooran, Asif, Watson, Haddin, Shadab, Misbah, Sami, Irfan, Rumman, Amad
ISLAMABAD WIN TOSS, BOWL FIRST
Islamabad United captain Misbah-ul-Haq has won the toss and elected to bowl first.
KINGS NEED TO ROAR LOUDER THAN EVER
It’s about time West Indian power-hitter Chris Gayle slogs for sixes all around the ground. It’s about time Sri Lankan veterans Mahela Jayawardene and Kumar Sangakkara put on display the most stylish of their strokes. It’s about time Mohammad Amir runs through the opponent line-up with his blistering pace.
It’s time for the Karachi Kings to roar as fiercely and as loud as possible.
With the stars they have got on their disposal, the Kings just cannot let defending champions Islamabad United tame them yet again as the sides clash in the Pakistan Super League (PSL) second playoff at Sharjah.
United got the better of the Kings in the corresponding fixture last year.