Jack Grealish made his Manchester City debut from the bench but it was another substitute, Kelechi Iheanacho, who won the Community Shield for Leicester.
Just two days after becoming the most expensive British player following his move from Aston Villa for £100million, Grealish was named among the City substitutes at Wembley.
The England attacker entered the fray with 65 minutes gone but was unable to help City break the deadlock.
Leicester responded by bringing on two of their summer signings, Patson Daka and Boubakary Soumare, with 20 minutes remaining.
Daka, the Zambia striker from RB Salzburg, was denied by Steffen who bravely dived at his feet on the edge of the box.
But Leicester would not be denied and their winner arrived after Nathan Ake clumsily brought down Iheanacho in the area, the striker beating Steffen to send the Leicester fans wild.
