Mikel Arteta described Arsenal's first Premier League defeat of the season as a significant reality check for his reigning champions. The Gunners were beaten 3-0 at Brighton on Saturday, ending a nine-match winning run in the league that stretched back to April.

Arteta said his team knew the challenge at the Amex Stadium would be tough but failed to meet it. "I think they knew, I think we knew how tough it was going to be today, and the first thing that we had discussed was about the first part," the manager told reporters after the match. The loss leaves Arsenal second in the table with 12 points from five games, three points behind leaders Manchester City.

The performance was a stark contrast to the defensive solidity that defined their title-winning campaign. Last season, Arsenal conceded the fewest goals in the division and did not lose by more than a single goal in any league match. Against a Brighton side that is the Premier League's top scorer with 16 goals, they looked uncertain at the back and lost control in midfield. They also created little in attack, failing to recover after going 2-0 down at half-time, a deficit from which they have not won a league game since March 2008.

Former England striker Alan Shearer was scathing in his assessment. "They absolutely battered Arsenal. How many times have we said that recently?" he said. The 3-0 scoreline marked Arsenal's heaviest defeat while holding the top-flight title since 1989.

The defeat interrupts what had been a perfect start of seven wins in all competitions this term. Before the Brighton game, Arsenal had conceded just one goal in their first four league matches. Key defender William Saliba was absent through injury, and the team's top scorer this season is Bukayo Saka with three goals.

Arteta's side spent around £200 million in the summer transfer window and had 15 players feature at the recent World Cup, but the collective performance in Sussex fell well short of expectations. They must now regroup ahead of their next Premier League fixture, a home game against fifth-placed Leeds United on 10 October. The full schedule is available on our fixtures page. The immediate task is to address the issues exposed by a well-drilled Brighton, managed by Fabian Hurzeler, who scored through Pascal Groß, Charalampos Kostoulas and Chema Andrés.

More detail at BBC Sport Football