English FA Cup holders, Arsenal, were stunned 4-2 by second-tier Nottingham Forest in the third round on Sunday.
Eric Lichaj scored twice for the hosts either side of a Per Mertesacker equaliser to give Forest a 2-1 half-time lead.
Ben Brereton, one of seven players aged 23 or under in the Forest side, made it 3-1 from the penalty spot in the 64th minute.
Danny Welbeck took advantage of an error to pull a goal back for Arsenal with 12 minutes left but Forest were awarded another penalty kick which Kieran Dowell converted.
It is the first time Arsenal have lost in the third round since 1996 and the first time since Arsene Wenger took over.
Wenger, serving the first of a three-match touchline ban, was forced to watch from the stands as Forest tore through his four-man Arsenal defence from the off.
Mertesacker’s last appearance in the FA Cup had seen him snuff out Diego Costa as Arsenal won the 2016/2017 final in May.
But this time he was being left hopeless by 18-year-old Brereton.
Wenger, in his post-match reaction, noted that his team’s performance was not good enough.
“We played a very good Forest team who were sharp and focused. The challenges were decisive. Overall, our performance wasn’t good enough.
“We have many players on the edge and we play again on Wednesday. When you don’t win, the selection is always questioned.
“I believe we had an experienced team — eight or nine internationals. It would be easy to think that was the problem.
“When you’re against a team like that, they’re very difficult to beat. Defensively you cannot afford the mistakes we made,” he said.
On being banned from the touchline Wenger said: “It was very frustrating and unfortunately it was a case on top of that of seeing the team lose.”
Gary Brazil, Nottingham Forest’s caretaker manager, in his post-match reaction said his team deserved to beat the Cup holders.
He added that the club’s goal was to strive to be in the English Premier League.
“This has got to be something we build on. This football club should be playing against the Arsenals of this world, and they should be beating them.
“These fans deserve to be watching Premier League teams and that’s what we’ve got to drive towards,” he said.
In other FA Cup matches played earlier, Harry Kane scored twice in two second-half minutes as Tottenham broke AFC Wimbledon’s resistance to beat the League One side 3-0.
Defender Jan Vertonghen made it 3-0 in the 71st minute with a deflected long-range strike for his first goal since October 2013, and for his team to reach the fourth round.
Also, Shrewsbury Town held Premier League side West Ham to a goalless draw at Montgomery Waters Meadow.
The hosts, who are second in League One, dominated for large parts of the game but were unable to find the winner, while West Ham could only register two shots on target.