Awesome Alexis Sanchez inspired Arsenal to their first win of the new season.
The Chilean scored, won a penalty and provided an assist as Arsene Wenger's men continued Watford's poor start to the new campaign.
Arsenal were 3-0 up and in cruise control by half time. They led after just nine minutes when referee Kevin Friend correctly penalised Nordin Amrabat for jumping into the back of Sanchez.
Santi Cazorla rifled the resulting spot-kick down the middle for 1-0.
Sanchez struck for his first goal of the season when he connected with an in-swinging ball across the box from Theo Walcott. Sanchez initially appeared to get the ball caught under his heels but sent it in while falling over.
Arsenal grabbed their third after Watford keeper Heurelho Gomes had produced a fine, one-handed save to keep out Theo Walcott.
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