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 have 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 is still some way from the glory days of Brian Clough, who led Forest to the English title in 1978 and two European Cups in 1979 and 1980.
“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.
AFP
