Winners of this competition in 2014, 2015 and 2016, Sevilla took another stride towards glory after resisting heavy pressure from United in this semi-final.
United went ahead with a Bruno Fernandes penalty, but former Liverpool fringe player Suso levelled for Sevilla.
And De Jong connected sweetly with a cross swung over by Jesus Navas in the 78th minute to send Julen Lopetegui's side through to Friday's showpiece.
United took a ninth-minute lead when Fernandes showed a familiar swagger in driving his penalty past Yassine Bounou, after a shabby challenge from Diego Carlos on Marcus Rashford.
Sevilla were not waiting long for their equaliser, though. It came in the 26th minute, with Suso driving past David de Gea after left-back Sergio Reguilon broke forward and crossed low and out of reach of United's defenders.
Anthony Martial, Rashford, Fernandes and Mason Greenwood all had great openings for United, who dominated large parts of the game but could not put away a goal in open play.
Bounou was outstanding, and there were concerns for United when Sevilla asked for a penalty as a free-kick from Joan Jordan hit Fernandes on the elbow.
Sevilla were out of luck then but the winner soon arrived, with United’s defenders switching off.
De Jong was a Premier League flop during a short spell at Newcastle United six years ago, and he was only a substitute on this occasion after a goal drought.
But he would prove the Sevilla hero, half-volleying home the precise delivery from former Manchester City winger Navas.