Crystal Palace manager Sam Allardyce
And Allardyce says he targeted the space left by Arsenal's full-backs.
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Palace took the lead through Townsend
Cabaye scored a wonderful goal to make it 2-0
He said: "I think the weaknesses of Arsenal have been defensive, because they leave Mustafi and Gabriel really exposed, Monreal and Bellerin play like wingers, they come inside with the centre forward, and the defenders are just left on their own.
"So if you can get at them you can get into the box and make chances."
Arsenal went behind after just 17 minutes when Andros Townsend tapped in Wilfried Zaha’s cross.
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Milivojevic converted from the penalty spot for 3-0
Yohan Cabaye then expertly curled home a second after the break, before Luke Milivojevic made it 3-0 from the penalty spot.
"Tactically the players were aware of how to beat Arsenal. The first thing was to defend and frustrate them, keep them playing sideways, then use the space behind the full-backs. Arsenal have been weak defensively, they leave the centre-backs exposed," Allardyce added.
"We won a lot of possession off them and created lots of chances. Cabaye's goal, what a finish – and that was down to us pressing them. It wasn't a shock for me because we played Chelsea and won that game. The result might be a shock, but we did that again and did it better.
"We all know Arsenal are going through their worst spell for years, but the only way to take advantage is by playing well. Everything worked perfectly for us today."
The result moves Palace six points clear of the relegation zone, while it dents Arsenal’s hopes for a top-four finish.