Arsenal boss Arsene Wenger was delighted with victory at Watford.
An early Santi Cazorla penalty was added to by Alexis Sanchez and Mesut Ozil as the Gunners raced into a commanding first-half lead at Vicarage Road.
They visibly tired after the interval and Watford pulled a goal back as club-record signing Roberto Pereyra scored a debut goal, but the hosts could not find a way to set up a grandstand finish.
"I think overall the performance was a strong one," he said.
"Very fluent and a massive first half. We were 3-0 up at half-time and in the second half we still created many chances but we missed something in the final ball, like we did at Leicester.
"We are not capable in the end to maintain completely for 90 minutes exactly the same intensity physically, but overall it's a very encouraging performance and a good win."