Heading to the Amex Stadium on Saturday afternoon, there was a sense of invincibility about Arsenal.

While questions in the week about whether the Gunners could go unbeaten this season were premature, it really was difficult to see Mikel Arteta’s side losing.

They had won nine Premier League matches in a row and were aiming to win ten on the trot for the first time since 2002.

Alas, the Seagulls are a side in form. Fabian Hurzeler’s team did a number on Coventry City a week ago and came back from two goals down to defeat Manchester United in midweek.

Well, on this occasion, it was the Premier League champions who were undone.

What went wrong for Arsenal against Brighton?

The worst performance of the Arteta era? It felt like it. Arsenal weren’t just pecked by the Seagulls on Saturday, they were mauled.

This always felt like a tricky away game. It may well go down as one of the most difficult they will face all season.

Yet, the Gunners have already faced tricky ties on the road this term – notably Sunderland and Napoli – and passed them with flying colours.

On the south coast, they did not come away with any positives. This was a dire result and one that will serve as something of a reality check heading into the international break.

Courtesy of a gorgeous hit from Pascal Gross in the first half, Brighton took the lead. Arsenal didn’t get out to the German quickly enough before he hit a sweet strike that struck the post and flew in.

The visitors were undone in similar fashion to make it 2-0. This time it was big Greek striker Charalampos Kostoulas. Once again it was a long-range strike that did the trick.

Warning signs had been there, though. Arsenal were so sloppy in possession and try as they might, they found it increasingly difficult to play through an aggressive Brighton press.

The third goal after half-time really rubbed salt into the wounds. The champions pride themselves on their set-piece routines but they were undone by one on this occasion.

Gross’ inswinging corner was met by the head of Chema Andres who scored his first Brighton goal.

Arsenal did create chances after that. Kai Havertz really should have scored a consolation goal but it rather summed up their fortunes in the final third on Saturday that he did not find the net.

Who is to blame for Arsenal’s defeat?

This was a wretched result and for many in the Arsenal team, they will go home this evening needing to take a long hard look at themselves.

A week ago Bruno Guimaraes scored a peach of a goal away at Sunderland but on his first Premier League start for the club, he really struggled.

He was guilty of giving the ball away in the first half that led to a Brighton chance and from that moment, the Brazilian never got into the game. He was hauled off on 60 minutes.

Skipper Martin Odegaard also didn’t last the 90 minutes. Hauled off on 73 minutes, his performance was labelled as an "absolute disgrace" by writer and podcast Adam Joseph on social media.

The Norwegian has been Arsenal’s player of the season so far having already netted four times in all competitions. As a result, this was easily his worst display of the campaign to date.

This was the Odegaard of last season, an Odegaard who couldn’t trust his right foot, a feeble looking Odegaard, a player who looked like the weak link.

Then again, not many in the attack, if anyone, covered themselves in much glory this weekend. The captain was constantly calling for players to make a run, only to be met by his teammates coming short. Havertz was guilty the most of that.

That said, the creative midfielder was anything but that on this occasion. During his 73 minutes on the pitch, he didn’t make a single key pass, nor did he attempt a single cross.

That was indicative of Arsenal’s performance. With Odegaard not on it, the Gunners were always going to struggle. A lack of crosses was also indicative of a team not willing to try something different. Brighton defended resolutely and were never going to let their opposition get in behind or play through the lines with ease.

This really was the Odegaard of last season. He didn’t win any of his three contested duels and his lack of influence was summed up by the fact that David Raya had more touches (58) than his tally of 47.

As the captain has shown already this term, he will have better days. This, however, was one of his worst in an Arsenal shirt.

There is no need to panic just yet but the performance, despite their woes in defence, only served to show why they needed to do more in the summer to strengthen their forward line.