The Spanish playmaker opened the scoring midway through the first half in the traditional curtain-raiser to the English season.
Aaron Ramsey, who scored the winner against Hull in May, then made it 2-0 just before the interval for the Gunners.
French international Olivier Giroud came on at half-time and scored a stunning third for the Londoners.
The match ended 3-0 to Arsenal. The Premier League starts on Saturday.