Both FA Cup meetings have been far closer-fought affairs and Huddersfield's advantage from Clayton's free-kick lasted a little over two minutes.
His thunderous strike, the first shot on goal of the game, flew past a sluggish Kasper Schmeichel from 35 yards, but was cancelled out by a more workmanlike effort almost immediately.
Ritchie de Laet's header from an Anthony Knockaert corner was blocked, but not cleared, by Alan Lee and Keane poked home his first goal since joining on loan from Manchester United.
The rest of the first half failed to live up to a furious start with Leicester's Paul Gallagher half-volleying wide from distance before Scott Arfield swiped a shot over the top from distance at the other.
Leicester had enjoyed the majority of possession before the break, with French playmaker Knockaert looking particularly lively.
They began to turn possession into clear-cut chances after the break as David Nugent nodded into Ian Bennett's gloves and Marko Futacs miss-kicked in the penalty box.
Huddersfield's counter-attacks were rare but dangerous and Scannell set up Arfield for a snap shot before his own strike sealed the game.
The winger shrugged off the attentions of Keane and Paul Konchesky as he cut in off the byline and slipped a shot between the legs of the advancing Schmeichel.
Substitute Jamie Vardy came closest to finding a second equaliser, but the expected onslaught never gathered any momentum as Huddersfield retained the ball, ran down the clock and booked their place in the next round.
View from the dressing room
Leicester boss Nigel Pearson:
"We were not good enough in both boxes. That is what cost us. We should have avoided giving away the free-kick for the first goal and were then caught on the counter-attack to concede the second. We were not clinical enough in their penalty area when we had our chances.
"We are disappointed to be out of the FA Cup but I have got a lot of faith in this group of players. The league has always been our priority but I would still have preferred to go through tonight."
Huddersfield's caretaker boss Mark Lillis:
"This was a fantastic evening for the club. The big thing was to get the lads into the dressing room at half-time and make sure they continued to believe in themselves. That was the big word - belief.
"It is great to be in the fifth round of the FA Cup and at home, and it will be great to pass it on to the new man if he is here. We have had a lot of adversity since I came into the job three weeks ago and we had a young side out there tonight, but they did us proud."
Lloyd Dyer concedes a free kick for a foul on Adam Clayton. Direct free kick taken by Ian Bennett.
Unfair challenge on James Vaughan by Lloyd Dyer results in a free kick. Free kick taken by Sean Scannell.
Paul Gallagher takes the chance to get an effort at goal and missed to the right of the net.
Paul Konchesky fouled by Sean Scannell, the ref awards a free kick. Free kick taken by Kasper Schmeichel.
The ball is crossed by Paul Gallagher, Header by Jamie Vardy from deep inside the penalty area misses to the left of the goal.
Kasper Schmeichel restarts play with the free kick.
Booking Caution for Anthony Knockaert.
Foul by Paul Dixon on Anthony Knockaert, free kick awarded.
Free kick awarded for an unfair challenge on James Vaughan by Michael Keane. Anthony Gerrard restarts play with the free kick.
Paul Konchesky has an effort at goal from long range that goes wide left.
Substitution (Huddersfield) makes a substitution, with Oscar Gobern coming on for Chris Atkinson.
Oliver Norwood crosses the ball from the free kick right-footed from right channel, save by Kasper Schmeichel.
Substitution Richie Wellens leaves the field to be replaced by Lloyd Dyer.
Booking Booking for Paul Gallagher for unsporting behaviour.
Paul Gallagher gives away a free kick for an unfair challenge on Adam Clayton.
74:16 Goal scored
Goal - Sean Scannell - Leicester 1 - 2 Huddersfld Sean Scannell grabs a goal from close in to the bottom right corner of the goal. Leicester 1-2 Huddersfield.
Paul Konchesky takes the free kick.
Substitution David Nugent leaves the field to be replaced by Jamie Vardy.
Substitution Martyn Waghorn joins the action as a substitute, replacing Marko Futacs.
Booking Anthony Gerrard goes into the referee's book.
Anthony Gerrard challenges Anthony Knockaert unfairly and gives away a free kick.
Paul Gallagher challenges Adam Clayton unfairly and gives away a free kick. Adam Clayton crosses the ball from the free kick right-footed from right channel, Kasper Schmeichel makes a save.
Substitution Alan Lee goes off and James Vaughan comes on.
The ball is delivered by Sean Scannell, Scott Arfield takes a shot. Save by Kasper Schmeichel. Inswinging corner taken right-footed by Oliver Norwood from the left by-line, clearance made by Anthony Knockaert.
Centre by Anthony Knockaert, David Nugent takes a shot. Save by Ian Bennett.
Substitution (Huddersfield) makes a substitution, with Oliver Norwood coming on for Jordan Sinnott.
Paul Gallagher takes a short corner.
Anthony Knockaert takes a shot. Ian Bennett makes a save.
Anthony Knockaert challenges Adam Clayton unfairly and gives away a free kick. Anthony Gerrard crosses the ball in from the free kick, save by Kasper Schmeichel.
The ball is crossed by Anthony Knockaert.
Jordan Sinnott takes a outswinging corner to the near post, save made by Kasper Schmeichel.
Richie Wellens concedes a free kick for a foul on Jordan Sinnott. The free kick is delivered right-footed by Adam Clayton from left channel, Wes Morgan manages to make a clearance. Inswinging corner taken from the right by-line by Jordan Sinnott, clearance made by Marko Futacs.
Richie Wellens produces a left-footed shot from just outside the penalty box that misses to the left of the goal.
Marko Futacs challenges Ian Bennett unfairly and gives away a free kick. Ian Bennett takes the direct free kick.
Inswinging corner taken by Paul Gallagher, Anthony Gerrard makes a clearance.
The referee blows his whistle to start the second half.
45:00 +1:28 Half time
Half Time The referee calls an end to the first half.
Free kick awarded for an unfair challenge on Marko Futacs by Anthony Gerrard. Paul Konchesky restarts play with the free kick.
Murray Wallace takes a shot. Save by Kasper Schmeichel.
Sean Scannell fouled by Paul Konchesky, the ref awards a free kick. The free kick is swung in right-footed by Adam Clayton, clearance by Michael Keane.
Shot on goal by Scott Arfield from long range goes harmlessly over the target.
Paul Dixon concedes a free kick for a foul on Anthony Knockaert. Free kick taken by Kasper Schmeichel.
Outswinging corner taken by Jordan Sinnott from the left by-line, clearance made by Michael Keane.
The official flags David Nugent offside. Ian Bennett takes the free kick.
David Nugent is flagged offside by the assistant referee. Anthony Gerrard takes the free kick.
Marko Futacs challenges Murray Wallace unfairly and gives away a free kick. Ian Bennett restarts play with the free kick.
Paul Gallagher takes a shot from long range which goes wide right of the target.
Matty James gives away a free kick for an unfair challenge on Murray Wallace. Scott Arfield takes the free kick.
The ball is delivered by Anthony Knockaert, save by Ian Bennett.
Unfair challenge on Paul Dixon by David Nugent results in a free kick. Ian Bennett takes the direct free kick.
Jordan Sinnott has an effort at goal from the edge of the area that misses to the right of the target.
Wes Morgan fouled by Sean Scannell, the ref awards a free kick. Paul Gallagher takes the direct free kick.
Inswinging corner taken left-footed by Anthony Knockaert, Paul Gallagher has an effort at goal from just outside the box which goes wide of the left-hand post.
Corner taken left-footed by Anthony Knockaert from the right by-line, clearance made by Alan Lee.
Foul by Calum Woods on Anthony Knockaert, free kick awarded. Free kick taken by Paul Konchesky.
Calum Woods concedes a free kick for a foul on Anthony Knockaert. Free kick taken by Paul Konchesky.
Free kick awarded for an unfair challenge on Paul Gallagher by Paul Dixon. Kasper Schmeichel takes the free kick.
6:36 Goal scored
Goal - Michael Keane - Leicester 1 - 1 Huddersfld Michael Keane fires in a goal from inside the six-yard box to the bottom left corner of the goal. Leicester 1-1 Huddersfield.
Paul Gallagher takes a shot. Clearance made by Murray Wallace. Anthony Knockaert takes the inswinging corner, assist on the goal came from Anthony Knockaert.
4:13 Goal scored
Goal - Adam Clayton - Leicester 0 - 1 Huddersfld Adam Clayton finds the net with a goal direct from the free kick from outside the area to the top right corner of the goal. Leicester 0-1 Huddersfield.
Sean Scannell fouled by Wes Morgan, the ref awards a free kick. Assist on the goal came from Sean Scannell.
The ref blows the whistle to begin the match.
Live text and data provided by The Press Association
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.