Chris Wood hit a first-half hat-trick as dominant Leicester sent Bristol City to the foot of the Championship.
Wood cut inside and drove home his first goal after 11 minutes, before pouncing on goalkeeper Dean Gerken's error to tap in his second.
Gerken looked culpable again as Wood's 20-yard shot squirmed under his body for the striker's hat-trick.
Matty James rifled into the corner just after the break to compound the woes of Derek McInnes' side.
Former Robins loanee Wood now has nine goals in his last five games, and six in three games since joining the Foxes in a £1m deal from West Brom.
Winger Ben Marshall provided the ammunition for the first goal, playing a precise pass that Wood controlled before firing home.
Leicester then capitalised on poor goalkeeping as Gerken failed to make sufficient contact on a punch, allowing Wood to tap in the loose ball.
Wood scored again just before the break, unleashing a shot that evaded Gerken to complete a quick-fire hat-trick.
Things got worse for the hosts when they sloppily conceded possession inside their own half, and James picked out the bottom-right corner to make it 4-0.
The hosts slowly stirred into life in the final 20 minutes, but Foxes keeper Kasper Schmeichel denied Paul Anderson and Liam Kelly.
The home crowd's warmest applause was reserved for the substitution of New Zealand international Wood in an acknowledgement of his superb display.
Leicester boss Nigel Pearson:
"Chris Wood has taken his chances for us and scored some early goals, which makes a big difference.
"He is a very focused young player who has fitted in straight away and gives us a height and physical presence up front, which perhaps we lacked.
"It is not easy to sign quality players in January and I am delighted to have secured him early in the window.
"We created a lot of chances to today and I am also very pleased to have kept a clean sheet."
Bristol City manager Derek McInnes:
"A lot of players let the fans down in the first half today.
"The first three goals were self-inflicted. Dean Gerken would say himself that he didn't have the best of games, but there were errors in front of him as well.
"We were too pedestrian in our play and made it easy for a very good Leicester team. I am looking to sign a few players before the transfer window closes.