Batting at No 5, Carter came to the crease at 104-3 in the 11th over, after opener Chad Bowes (57 off 31) had given the hosts a good shot at staying in the contest.
Captain Cole McConchie (49no off 25) began the re-launch, before the real fireworks came in an unbelievable 16th over, as Devcich saw his figures blow out to 0-61 off four.
Drag downs, full tosses, a strong breeze and a short boundary all played a part, but that was not to take away from Carter, who was just 11 off 12 balls before his stunning onslaught, going on to score an amazing 59 off his next 17, as he sent the required rate of around 14 per over tumbling with every meaty blow into the on-side.
Remarkably, in what was his 26th domestic T20 game, Carter held a previous score of just 35. And speaking to Sky soon after his heroics, he was still coming to terms with his achievement.
"Basically just stepped across and swung as hard as I could," he said of his game plan. "I'm not so sure I got many off the middle, but pretty short boundary there, so they just carried over, I was pretty thankful for that.
"We needed a big over at that time, it was sort of my job to just try and take down that end and I was lucky enough to get a few over there, so it was good."
Earlier, the Knights had posted 219-7 thanks to Seifert and Dean Brownlie (55 off 29) putting on a rapid 119 in exactly 10 overs.
McConchie and Andrew Ellis pulled things back, claiming two wickets apiece and going for around eight an over, but it still looked like they'd need something special to be able to pull off victory.
Lucky they had just the man for that.
The victory lifts the Kings off the bottom of the table, and with four games left they are still in the playoffs hunt.
AT A GLANCE
Northern Knights 219-7 (Tim Seifert 74, Dean Brownlie 55; Cole McConchie 2-33, Andrew Ellis 2-35) beat Canterbury Kings 222-3 (Leo Carter 70no, Chad Bowes 57, Cole McConchie 49no) by runs.
Meanwhile, the Canterbury Magicians have notched their first win of the women's Super Smash competition, and ended the finals hopes of the Northern Spirit.
Sitting bottom of the table after six of 10 games, the Magicians were already out of the playoffs picture, while the Spirit had to win this one at Christchurch's Hagley Oval on Sunday afternoon to be any chance.
But thanks to a calamitous batting collapse, the visitors were defeated by four wickets, as the Cantabs, who were runners-up last season, got home with three balls to spare.
Sent in, the Spirit had got to 30-0 in the fifth over, before their order was decimated, remarkably losing four wickets for no runs, then five for two in 11 balls.
Jacinta Savage (3-11 off four overs) struck with her first, third and fifth deliveries of her third over, while Lea Tahuhu (3-31 off four) also profited either side of that to decimate the visitors' lineup.
It was left to Brooke Halliday (43 off 37 balls) and Lucy Boucher (41no off 43) to rescue the innings, with the pair teaming for a 91-run sixth wicket stand and getting the Spirit through to 125-7 from their 20 overs.
In reply, Canterbury were comfortable, if not rapid, in their chase, keeping wickets in hand for the final overs.
Opener Frances Mackay (42 off 55) anchored things, before her runout in the 18th over ensured things stayed interesting till the finish.
Very next ball Laura Hughes launched a straight six to ease the home side's nerves, though she was then also runout next ball.
With five needed off the final over, Spirit captain Felicity Leydon-Davis snared a great caught and bowled first ball, but two deliveries later Gabby Sullivan guided a four to a vacant third man to seal victory.
AT A GLANCE
Northern Spirit 125-7 (Brooke Halliday 43, Lucy Boucher 41no; Jacinta Savage 3-11, Lea Tahuhu 3-31) lost to Canterbury Magicians 127-6 (Frances Mackay 42; Carolyn Esterhuizen 2-26) by four wickets.
