Arsène Wenger spoke about clarity and – perhaps inevitably – his subject was Alexis Sánchez. The Arsenal forward was not at the Emirates Stadium because, according to Wenger, he had driven north to put himself in position to complete his January transfer to Manchester United. Yet Sánchez still managed to colour the narrative.

Wenger talked about how the saga involving his club’s best player had affected everybody. “For us, it’s not only to lose a world-class player – it’s a period of uncertainty that creates a strange feeling in the dressing room,” the manager said. “What is very difficult is that, for the first time, we are losing one of our big players in January. It’s a bit more destabilising than usual.”

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Wenger put forward the silver lining. “Once things are clear, the team responds and focuses on the job,” he said. Sánchez had left the team hotel on Friday night and it now looks pretty certain that the next time he appears in these parts, he will be wearing a United shirt. Henrikh Mkhitaryan is primed to move in the opposite direction and Wenger said that part of the deal was affecting the timing of it all.

Against a Crystal Palace team that simply did not turn up at the outset, Arsenal stepped boldly into the post-Sánchez era. Wenger will always say that the pitch is the only place where anything matters and this was a reminder of what his team can do when it all clicks.

When Arsenal play like this – they were 4-0 up after 22 minutes – it begs the question as to why they can be so weak on other occasions.

Nacho Monreal was the unlikely star on his comeback from an ankle problem. He scored the opening goal and laid on the second and third before departing, as a precaution, on 33 minutes after a kick to his hamstring. Monreal was not the only Arsenal player who retuned from injury to good effect. Laurent Koscielny scored the third goal while Mesut Özil decorated the afternoon with some lovely touches, not least his flick for Alexandre Lacazette’s first goal in 10 games.

Roy Hodgson could not believe what he was watching. It was a day when virtually nothing went right for him and his Palace team, down to Yohan Cabaye being taken off on a stretcher with ankle ligament damage in the closing moments. It looked like yet another serious injury problem for the club.

Arsenal laid waste to Palace in an early bombardment and it was shocking to see how loose the visitors were at the back. Wenger’s team twisted the knife with relish. The game was over after only 13 minutes, when Monreal eluded James McArthur and ran around the back to meet Granit Xhaka’s corner. Monreal hooked into the danger area and Koscielny rolled home.

Monreal’s goal set the tone for both teams. McArthur let him go on a Xhaka corner and the defender advanced into yards of space to thump home his header. The goalkeeper, Wayne Hennessey, was caught in no man’s land. McArthur put his head in his hands. Palace were on their heels all too regularly and it was particularly pronounced on Arsenal’s second.

Timothy Fosu-Mensah stretched to cut out Alex Iwobi’s ball for Lacazette but when it broke Monreal was allowed to power into the left side of the area. He cut the ball back and Alex Iwobi, in so much space, swept past Hennessey from close range.

Facebook Twitter Pinterest Cyrille Regis is remembered at the Emirates Stadium. Photograph: Dan Weir/PPAUK/Rex/Shutterstock

Arsenal enjoyed themselves, pulling out the party tricks; Palace gasped for breath. The fourth was all about the interchange between Özil and Jack Wilshere. The final pass came from Özil – a sumptuous backheel – and Lacazette beat Hennessey for power.

It was a humiliation for Palace. Özil and Wilshere drew aahs with first-half flicks and the damage at the interval might have been heavier. Iwobi twice worked Hennessey while James Tomkins leapt into a saving block on 15 minutes to deny Xhaka.

Palace, who the have completed the signings of the defender Jaroslaw Jach from Zaglebie Lubin and the midfielder Erdal Rakip on loan from Benfica, were better after the interval, although they could hardly have been any worse. Wilfried Zaha wanted a penalty following a challenge from Mohamed Elneny while Bakary Sako found Christian Benteke with a glorious ball on the break. Benteke could not beat Cech when one-on-one.

Iwobi was again denied by Hennessey while Lacazette had a stoppage-time penalty appeal turned down after Tomkins jumped in on him. Palace’s consolation came when Luka Milivojevic took a touch on his chest, spun and found the far corner following Cabaye’s corner. It rang hollow.

Before kick-off, it emerged Arsenal had failed with a €50m (£44m) bid for the Borussia Dortmund striker Pierre-Emerick Aubameyang. Olivier Giroud has been mentioned as a possible makeweight in the deal.

Wenger made no comment, possibly fearing another ”tactical reaction” from the Dortmund sporting director, Michael Zorc. Arsenal did their talking on the pitch.