Postpublished at 20:43 Greenwich Mean Time 8 February 2017
Leicester 0-0 Derby
Oh, and none of the Derby players were caught picking their nose.
Ndidi and Gray score fantastic extra-time goals for Leicester
Foxes will travel to League One side Millwall in the fifth round
Watch clips of goals and key incidents on this page
Both sides named weakened teams (10 changes for Leicester, eight for Derby)
Jonathan Jurejko
Leicester 0-0 Derby
Oh, and none of the Derby players were caught picking their nose.
Leicester 0-0 Derby
Our cameras inside the Derby dressing room have been turned on. Steve McClaren is very animated, gesticulating and pointing his arms all over the place. I've no idea what it all means. Hopefully the Derby players do.
#bbcfacup
Andy Vickers: Lamentable team selection tonight. Meanwhile Dortmund v Hertha and both have full strength teams in their cup game.
Naveed Afzal: Is anyone planning on testing the keeper? Gray the only one with a little bit of quality. Dull game is putting it mildly
Leicester 0-0 Derby
To be fair the game's been played a relatively decent tempo. But there have been no chances and there is no atmosphere.
Match of the Day host Gary Lineker jokes he almost fell asleep in the first half...
Leicester 0-0 Derby
Time for a brew. That's probably the highlight of the hour.
Leicester 0-0 Derby
Have a pop! That's what Jacob Butterfield decides to do with time ticking down to half-time. The Derby midfielder cracks a low effort from 20 yards, forcing Ron-Robert Zieler into getting his gloves mucky for the first time. Good save.
Leicester 0-0 Derby
All eyes on the fourth official then. How many minutes of stoppage time? Two.
Leicester 0-0 Derby
This Nampalys Mendy lad likes a crunching tackle. The Leicester midfielder flies into a hard, but fair, tackle close to the halfway line, slapping the greasy turf in frustration that the ball flew out for a throw-in.
Leicester 0-0 Derby
The scoreline is still blank, as is the 'shots on target' column. Here's the closest we have come to a goal...
Leicester 0-0 Derby
Kevin Kilbane
Former Everton winger on BBC Radio 5 live
I'm loathed to say that outside the area that's a free-kick. It's a nothing ball in the penalty area. Outside the area it's an easy one to give. It was a foul though. There have now been two soft ones in the area.
Leicester 0-0 Derby
Graeme Le Saux
Former Chelsea left-back on BBC One
That, on first reflection, looked like a penalty to me. It’s a shove in the back. The more I see it the more I think it's a penalty.
Leicester 0-0 Derby
The more we see it, the more it looks like a penalty. A clear shove by Keogh. Lucky lad. And how it was a corner I'll never know - it hit Chilwell's legs last as he tumbles.
Leicester 0-0 Derby
Another half-hearted penalty appeal for Leicester. Derby skipper Richard Keogh leans into Ben Chilwell with his arm, the Leicester left-back hitting the deck quicker than a drunk sailor on a choppy sea. Ref Mike Jones waves him up and points for a corner.
Leicester 0-0 Derby
Don't think Ron-Robert Zieler or Jonathan Mitchell have dirtied their gloves yet. Easy street for both keepers.
Leicester 0-0 Derby
Have they stopped handing out those clackers at Leicester this season? I can't hear them. Although that isn't a bad thing. They became 2016's vuvuzela.
Leicester 0-0 Derby
Kevin Kilbane
Former Everton winger on BBC Radio 5 live
I just feel Ahmed Musa went with the wrong foot - he should have allowed it to hit his left foot.
Leicester 0-0 Derby
Yes! Leicester carve up Derby for their best opportunity of the game. Demarai Gray sticks on the gas to find space on the right, whipping in a delicious cross down the 'corridor of uncertainty' between keeper and defence. Ahmed Musa slides in but can't stick his toe on the ball. If only he was one shoe size bigger...
Leicester 0-0 Derby
Signs of encouragement for Leicester?
Leicester 0-0 Derby
Sorry, nothing to get excited about. Leicester win a corner, Marc Albrighton swings it in, ball flies over Yohan Benalouane's bald head.
Leicester 0-0 Derby
This is heading for extra time isn't it?! We've already come to that conclusion in the BBC Sport office. Oh wait...