Arsene Wenger paid the price for fielding a weakened team in the third round of the FA Cup, as they were embarrassingly dumped out by Championship side Nottingham Forest at the City Ground.
The Frenchman had to watch on from the stands because of his misconduct charge for his comments made to match officials against West Brom last weekend, as two goals from Eric Lichaj and two from Ben Brereton and Kieran Dowell handed caretaker manager Gary Brazil a famous win.
Forest were at the races right from the off as they tried to get in the faces of their Premier League opposition, adopting some high press tactics on Per Mertesacker, Mathieu Debuchy and Rob Holding in defence.
The home side took the lead in the 19th minute after Kieran Dowell fizzed in a free-kick from the right-hand side. Some clever positioning from Lichaj allowed him to stay onside to nod beyond Ospina from point-blank range.
Arsenal hit back only a few minutes later thanks to a good free-kick of their own. Theo Walcott clipped the ball into the danger zone from the left which was met by Rob Holding who hit the post. The ball rebounded into the path of Mertesacker who did well to control and finish in an instant.
The Gunners created little chances after that and faced a few nervy moments from Forest striker Ben Brereton, who gave the clunky Mertesacker the runaround for a lot of the half.
The Englishman cut inside the World Cup winner in one instance and stung the palms of Ospina, who thwarted Brereton again moments later after he sprung the offside trap down the left-hand side.
Forest then went ahead thanks to a sumptuous strike from Lichaj for his second of the game. The right-back wound up on the edge of the Arsenal box to collect a poor Holding headed clearance, chested it down and unleashed a dipping volley into the top corner with hardly any back-lift.
Arsenal tried to apply the pressure from the restart, penning Forest into their own half for large parts of the game. Ainsley Maitland-Niles and Reiss Nelson, in particular, were the bright sparks for the visitors, with more experienced heads such as Walcott, Danny Welbeck and Alex Iwobi offering little in terms of a goal threat.
Dangerman Brereton had another great chance to score when Tyler Walker crossed from the left-hand side. The striker connected but was being closely marked by Holding, which was one of the game's fascinating battles.
Holding then clumsily conceded a penalty on Matty Cash, giving Brereton the opportunity to score from the spot and put Forest in dreamland. The 18-year-old duly obliged and swept the ball home for the goal his performance thoroughly deserved.
Forest began to grow in confidence after the goal, but a mistake from Jordan Smith allowed the largely ineffective Welbeck to score in an open net after failing to gather a through ball.
That certainly set up a nervy final 12 minutes for the home side, but referee John Moss awarded the home side a penalty after Debuchy took down Armand Traore who was through on goal. Kieran Dowell was the man to step up this time and he scored after slipping into his kick.
Moss consulted with his linesman and controversially decided the goal should stand, and TV replays appeared to show Dowell may have kicked it twice.
The pulsating cup tie didn't let up there, and a red card was shown to Joe Worrall after he put a thudding challenge through the back of Chuba Akpom.
Moments later, Arsenal nearly made it 4-3 but for an amazing save from Smith to deny substitute Eddie Nketiah after David Vaughan's careless pass. The youngster attempted the chip which Smith managed to get a touch on, and Walcott wasn't fast enough to convert into an empty net as it trickled just wide and out.
Forest weathered the storm and ran out worthy winners, and for Arsenal, it is the first time in 21 years they have gone out in the third round of the FA Cup and the earliest they've ever exited the competition under the management of Wenger, who will surely have some difficult questions to field in the aftermath of remarkable game.