Arsenal lost their first English Premier League match of 2021/22 season to league newcomers, Brentford.
The hosts scored in both halves and could have scored more on a lucky day.
Brentford spent some 74 years away from the first tier and for at least one night they are top of the Premier League table.
The Bees got their first goal after 22 minutes when Sergi Canos drove low past keeper Bernd Leno at the near post.
Although Arsenal complained bitterly that the ball had gone out of play in the build-up, the match officials ruled that it was a goal.
Emile Smith Rowe and Nicolas Pepe, late on, were denied goals by Brentford keeper David Raya home fans exploded in noise and elation when they scored a second with 17 minutes left.
Arsenal, without strike pair Alexandre Lacazette and Pierre-Emerick Aubameyang through illness, paid the price for a hopeless attempt to defend substitute Mads Bech Sorensen’s routine long throw.
New £50m defender Ben White was particularly culpable as Christian Norgaard arrived to head home.
Brentford’s supporters, understandably, celebrated wildly at the final whistle, but this was a result and performance that instantly turns the spotlight on Arsenal manager Mikel Arteta as he desperately needs an improvement on last season.
Speaking after the match, Arteta refused to attribute the loss to the absence of his senior players saying they had what it takes to win the match against the Bees.
Meanwhile, the gunners will next play Chelsea, Manchester City, Norwich, Burnley, Tottenham then Brighton and Hove.