Nottingham Forest knocked holders Leicester out of the FA Cup as the Championship side powered to a shock 4-1 win, while non-league Boreham Wood upset second-tier Bournemouth with a 1-0 victory on Sunday.
Leicester's disappointing season hit a new low with the dismal fourth-round loss against their Midlands rivals at the City Ground.
Last season's Wembley triumph against Chelsea was Leicester's first-ever FA Cup final victory, but that seemed a distant memory as their trophy defence ended with a whimper.
"It is a really poor performance. This team has been together for three years and I see some worrying signs with some of the players," Leicester boss Brendan Rodgers said.
Bottom of the second tier when Steve Cooper took charge in September, Forest have been revitalised by the former Swansea boss and they destroyed Leicester with three goals in nine first half minutes.
Forest will face fellow Championship side Huddersfield in only their second appearance in the FA Cup fifth round in 17 years.
Having climbed to eighth place in the Championship, Forest are also chasing a return to the Premier League for the first time since 1999.
"It's a brilliant day for everyone. We are in the middle of trying to build something. I'm really pleased for the boys and proud of the club," Cooper said.
Forest took the lead in the 23rd minute when Brennan Johnson's cross was nodded down by Keinan Davis and poked home by Philip Zinckernagel.
Just 24 seconds later, the sell-out crowd erupted again as Leicester shot themselves in the foot.
Daniel Amartey's woeful backpass towards Leicester keeper Kasper Schmeichel was intercepted by Johnson, who took a touch before clipping his shot through the Dane's legs.
The goal prompted one angry Leicester supporter to run onto the pitch and confront several Forest players in an ugly incident that saw punches thrown before he was arrested.
In the 32nd minute, James Garner swung over a corner and Joe Worrall took advantage of Leicester's slack marking to head past Schmeichel.
Forest keeper Brice Samba gifted Leicester a goal in the 40th minute, needlessly rushing out of his area as Kelechi Iheanacho danced past him and shot into the empty net from an acute angle.
But Djed Spence exchanged passes with Zinckernagel before delivering a clinical finish in the 61st minute.
At Dean Court, Mark Ricketts' 38th minute goal sent Boreham Wood into the fifth round for the first time.
Boreham Wood, currently in fifth place in the fifth-tier National League, are the lowest ranked team left in the competition.
But Bournemouth, third in the Championship, paid the price for a lethargic display that suggested they were prioritising their push for promotion to the Premier League.
Boreham Wood, yet to concede a goal in this season's FA Cup, will face Everton in the last 16 at Goodison Park.
"I'm on top of the world, the emotions at the minute are incredible. They are unbelievable these boys," Boreham Wood boss Luke Garrard said.
Jurgen Klopp labelled Harvey Elliott's goalscoring return in Liverpool's 3-1 win over Cardiff as a "fairytale" after five months out with a serious ankle injury.
Elliott was introduced off the bench alongside new signing Luis Diaz after Diogo Jota's header had opened the scoring early in the second half.
Diaz made an instant impact by teeing up Takumi Minamino to double Liverpool's lead at Anfield.
But the biggest cheer was reserved for Elliott when he fired home on the volley 14 minutes from time.
There were fears Elliott could be out for at least the rest of the season when he suffered a dislocated ankle against Leeds.
"Coming on was a great step back but scoring this goal was a proper fairytale," said Klopp.
Rubin Colwill pulled a goal back for the Bluebirds, but it is Liverpool who will host Norwich in the last 16.
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