Phil McNulty, BBC chief football writer
Forest already have the pressure of being referred to an independent commission by the Premier League for alleged breaches of financial regulations, but it was on-field mistakes that played a crucial part in their 2-1 loss at The City Ground.
Nuno Espirito Santo's side were rarely an attacking threat but had at least kept Arsenal at bay until keeper Matt Turner allowed Gabriel Jesus' routine shot to squirm between his legs at the near post as the deadlock was broken in the 65th minute.
Gonzalo Montiel then lost possession in the build-up to Arsenal's second from Bukayo Saka and it was game over, despite substitute Taiwo Awoniyi's late goal giving the Gunners their first anxious moments.
If there was a bonus for Forest from this night, it was the return of Awoniyi as a substitute for the second half, his lively performance suggesting he could be an important presence in the tough weeks ahead.