Jamie Vardy scored a 90th-minute winner for Leicester to break Sheffield United hearts and leave them in a perilous position at the bottom of the Premier League table.
The Blades looked set to secure only their second point of the season when Oli McBurnie scored his first of the campaign after Ayoze Perez had given the visitors the lead.
However, the Foxes never looked like wanting to settle for a point in their pursuit of a Champions League spot. With moments of the match remaining, James Maddison fed in Vardy, who scampered clear of the home defence and slotted his shot past Aaron Ramsdale.