After normal and extra time finished 1-1, the two sides went to spot kicks and Sporting KC survived giving up a 2-0 lead and Graham Zusi's miss for the title, as Lovel Palmer's penalty for Salt Lake - the 20th of the shootout - came back off the crossbar to give the hosts the title at Sporting Park in Kansas.
Sebastian Velazquez also had a spot-kick to win it for Real but Sporting goalkeeper Jimmy Nielsen proved himself a hero with a diving save to prolong the shootout.
Earlier, Alvaro Saborio gave Salt Lake a 52nd-minute lead as Jason Kreis' men closed on what would have been a second title in five seasons.
But Sporting KC, the Eastern Conference champions, responded when Aurelien Collin nodded home an equaliser in the 76th minute from a Zusi corner.
The equaliser came just three minutes after Javier Morales' chipped effort on goal was denied by the crossbar, with Salt Lake an inch away from a two-goal lead.
Saborio thought he had fired the visitors 2-1 up in the 105th minute, as he headed home at the far post but the linesman correctly called the Costa Rican front man offside.
That would be the best chance for either side to score in the additional half-hour, as the final - for the third time in MLS history - went to a shootout.
Real's title in 2009 came via a shootout win over the Los Angeles Galaxy but if the first four penalties were anything to go by, they would not end this one well.
Claudio Bieler and Paulo Nagamura both slotted their attempts for Sporting KC, while Saborio scooped his attempt over the bar and Ned Grabavoy had his shot saved by Danish goalkeeper Nielsen and the hosts had one hand on the title.
However, it would not be so easy for Peter Vermes' men, as Salt Lake's comeback started immediately - with goalkeeper Nick Rimando, man of the match in RSL's 2009 final victory, saving Matt Besler's penalty.
Kyle Beckerman, who teed up Saborio for Real's goal in regulation, cut the deficit to one as he converted Salt Lake's first goal in the shootout.
Benny Feilhaber made it 3-1 to Sporting, but only just as Rimando got a hand on his straight, high attempt.
Jimmy Plata kept Salt Lake alive by converting his attempt before Zusi stepped up and put his spot kick over - clipping the crossbar on its way into the stands.
Javier Morales then made it 3-3, sending the shootout to sudden death - where Real would blow a chance to win the title themselves.
Velazquez could have made Sporting's Lawrence Olum pay for his miss wide, however the former had his effort saved by Nielsen.
The two sides traded goals again, and regulation-time goal-scorer Collin made it 7-6 with a fine finish - before Palmer failed to convert to send the home fans into raptures.
The result sealed Sporting Kansas City's second MLS title, after their maiden win in 2000, when they were known as the Kansas City Wizards.
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