Arsene Wenger suffered a first ever FA Cup third-round exit as managerless Championship side Nottingham Forest stunned holders Arsenal at the City Ground.
The home side took the lead after 20 minutes as Eric Lichaj headed home from close range, although the advantage lasted just three minutes as Per Mertesacker followed up after Rob Holding’s header had struck the post.
Lichaj reclaimed the lead for Forest – led by caretaker boss Gary Brazil – with the American defender scoring a spectacular dipping volley from the edge of the area a minute before half-time.
Forest pulled further clear in the second half when Ben Brereton sent David Ospina the wrong way from the penalty spot after Holding upended Matty Cash.
Danny Welbeck reduced the deficit for a much-changed Arsenal with 11 minutes remaining after Forest goalkeeper Jordan Smith failed to hold a through-ball.
Arsenal’s first defeat in the third round since losing a replay 1-0 to Sheffield United in January 1996 was confirmed courtesy of Kieran Dowell’s 85th-minute penalty, before Joe Worrall was shown a straight red card for the home side in the closing stages following a late tackle.