In a week where Arsenal seemed to have started to establish a new era under Unai Emery with a statement victory in Naples, Sunday showed old habits still linger at the Emirates Stadium.
A ten-match winning streak and unbeaten home record since the opening day, ended by a ruthless Crystal Palace who celebrated guaranteed Premier League football for next season. It was a day which had seen Manchester United dismantled at Everton, after Tottenham Hotspur slipped up the day before, meaning Arsenal would move into third with a win.
But in this week, of all weeks, football has shown it doesn't tend to follow a script. Perhaps the number of rotations by Emery disrupted the side, maybe it was a hangover from a hectic week, or it was just complacency that they could go through the motions and still win. Whatever the conclusion, the defending from the Gunners here was 'school-boy' to say the least and leaves them with even less room for error in hopes of a top four spot.
It must also be said, Palace were fearless and could've easily had more with the chances they were presented with in the first half. Roy Hodgson has now toppled Manchester City and Arsenal on their travels, drew with United and taken Liverpool all the way.
Shkodran shocker leads defensive collapse
Everyone associates Arsenal, particularly in recent years, in having incapable defenders. Despite that stereotype, and it being proven right on occasions, the Gunners had actually only conceded once in their seven games leading up to Sunday, surprising right.
The performance in their Europa League victory in Naples was commanding, professional and confident, a huge step under Emery not only in the competition but showing the progression as a unit. At home they had conceded the same amount of goals as City, 12, and one fewer than Spurs, impressive.
So, what on earth happened against Palace, in what was a complete defensive capitulation to end up 3-1 down?
Firstly, Emery changed up the backline which clearly didn't look comfortable together in the first half and made it a tense and lacklustre showing from the hosts. Laurent Koscielny and Sead Kolasinac maintained their presences and looked like the only ones maintaining their composure.
Dinos Mavropanos has been sidelined the majority of the season and looked shaky, an unfortunate case of being thrown in due to suspensions and fatigue. Likewise, Carl Jenkinson hasn't been in the first-team picture, making just his third Premier League start and showing rustiness, Ainsley Maitland-Niles showed his value with an effective second-half performance in his place. Then there was Shkodran Mustafi, who pretty much had a day to forget.
If you look at the stats, Mustafi has more interceptions, tackles and aerial success than Sokratis and Koscielny, so he must be doing something right. However, Arsenal have conceded 32 when the German plays, six more than Sokratis and double of Koscielny, as well as Mustafi conceding two penalties at crucial points to cost Arsenal wins over Spurs and in the reverse with Palace.
He is culpable to hapless errors. The Eagles' first goal is a free-kick floated into Christian Benteke, who is unmarked to head home with ease, the man marking him, Mustafi. The defender is appealing for offside as the ball is in the air rather than trying to stop the forward. Chances for Benteke and Cheik Kouyate go to waste, by the hour mark Arsenal have recovered the deficit and seem in control at last.
The following ten minutes won the game for Palace, and may prove costly in Arsenal's chase for the Champions League spots. Mustafi, in bizarre fashion, steps away from Wilfried Zaha to allow him to go one-on-one and score, he believed it was Bernd Leno's fault. By this point the home crowd are restless, the third is another set piece. That man Mustafi is in the centre of things again, seeming to leave James McArthur unmarked to put Palace out of sight.
To compound the misery of the one-time World Cup winner, he is booked for diving.
Eagles rise up away from home
For years there'd always be some trepidation of going to Selhurst Park, in the same way people talk about Goodison Park or a few years ago, playing Stoke City away.
Yet, Palace have been a shadow of themselves in front of the home support this season, winning just four and scoring a measly 14 goals, only five more than Huddersfield Town. Whilst on their travels, they are a tough opponent.
A historic win at the Emirates follows defeating champions City with a goal of the season from Andros Townsend, drawing 0-0 at Old Trafford, a ruthless 4-1 win at Leicester City and defeating Wolverhampton Wanderers 2-0.
Hodgson's team seem more fluid away from home, able to sit back and hit on the counter-attack, Zaha being integral to their successes. He draws fouls so often and is a vital outlet for the team, he was fouled five times including for the free-kick which led to McArthur's goal.
He has often been their leading line, but with Benteke ending his goal drought of 19 games and showing his physical prowess again, he could still blossom in a partnership with the dynamic Zaha. At the other end, they've conceded the same amount as United away, 28, and only six more than Spurs.
A talisman of their defence, Aaron Wan-Bissaka. He made the most ball recoveries, 11, and interceptions, eight, on Sunday, especially important given Arsenal's utilisation of Kolasinac down the left wing. He had a 100% tackle success in the first half, a factor in him being the best tackling defender in the league and one of the best in Europe, 120.
In Zaha and Wann-Bissaka, they have two popular properties and Hodgson will be insistent on their futures staying with Palace. Hodgson told the BBC, he believes he (Zaha) is 'happy at Crystal Palace', despite his admission that he wants to be playing Champions League football.
A first win in 25 years at Arsenal, Palace fans really will be 'glad all over'.
Emery needs backing in the window
It wasn't going to be a quick-fix, but considering the lack of resources compared to their rivals, Emery has had a very good first season at Arsenal.
In fourth place and Champions League football in their hands, along with a Europa League semi-final, any Gunners supporter would've bitten your hand off in August.
But the strength of the squad was displayed on Sunday, and there are deficiencies. Arsenal's two Premier League defeats in nine, have come when Granit Xhaka has been missing. As much as he has been scapegoated since his arrival, he has immensely improved under Emery, losing just two of 22 games when he has played in midfield.
His control of possession and link-play to the likes of Mesut Ozil, Alexandre Lacazette and Kolasinac was a huge miss. That is back-to-back defeats in the league when Mohamed Elneny and Matteo Guendouzi have started together, their limitations with and without the ball horribly exposed Arsenal to Palace's swift attacking play.
The presence of Sokratis was another glaring factor, they had conceded just once in seven games when has completed the 90 minutes alongside Koscielny. Arsenal may scrape into the top four or grind their way to the Europa League this season, but it'll be a short-term success, they need to build on in the summer to improve.
Emery rotated too much and it cost the Gunners, but it may be a blessing for him and the hierarchy as the problems were on show and need for defensive recruitment especially, was highlighted.
It's not a disastrous defeat for Arsenal, but they can't slip up again in the race for the top four. Palace take the pride from a London Derby this weekend.