Darren Bent scored a goal at both ends before Leicester City captain Wes Morgan salvaged a 2-2 FA Cup draw for the off-colour Premier League champions at Derby Country.
After Bent atoned for a moment that will become a classic of future bloopers compilations, Craig Bryson had Championship Derby dreaming of a notable fourth-round scalp and ample east Midlands bragging rights.
Claudio Ranieri's men remain some way short of the levels they hit last season, but Morgan, one of the heroes of that famous title triumph, stepped up to spare the Foxes blushes four minutes from time.
Leicester started with the greater purpose and had the lead in bizarre fashion from an eighth-minute corner as an apparently panicked Bent managed to slice into his own net when trying to hack the ball to safety.
The former England striker showed himself to be much more at home in the opposition penalty area when he glanced Will Hughes' right-wing cross beyond Kasper Schmeichel and inside the far post.
Derby went in front five minutes before half-time as Bryson burst into the box and coolly picked out the bottom corner for his first goal of the season.
Ranieri sent winger Demarai Gray on for full-back Christian Fuchs at half-time and he was denied an equaliser at point-blank range by Derby goalkeeper Scott Carson before striking the base of the post.
Carson got himself in the way of Shinji Okazaki's follow-up on that occasion and his colleagues might have made the tie safe before the hour when Johnny Russell nodded into the side-netting, undone by an awkward bounce.
Leicester's second-half pressure eventually told, with Morgan powering home as the impressive Gray supplied the corner.
Derby substitute Abdoul Camara jinked into the box upon his introduction and had penalty appeals waved away when his eventual shot struck Robert Huth's arm, while Carson concluded a busy evening by denying Danny Drinkwater in stoppage time and securing a return match at the King Power Stadium.