Leicester's defence of their Premier League title began with a shock defeat at newly promoted Hull, who are managerless and relegation favourites.
Under caretaker boss Mike Phelan, Hull took the lead when Adama Diomande and Abel Hernandez combined acrobatically, with Diomande awarded the goal.
Riyad Mahrez replied from the penalty spot at the start of the second half after Demarai Gray had been fouled.
But Robert Snodgrass earned the Tigers victory after a cross was not cleared.
Danny Simpson's clearance from Ahmed Elmohamady's ball into the area only found Snodgrass on the edge of the box, and he drilled home.
It is the first time the reigning English champions have started the season with a defeat since 1989, when Arsenal lost at Manchester United.