Arsenal claimed a third consecutive win on their Asian Tour, outclassing Nagoya Grampus 3-1 at the Toyota Stadium.
Despite Kisho Yano's late consolation it was an accomplished performance from Arsene Wenger's side, who look in good shape despite their lack of summer signings.
Japanese outfit Grampus were supposed to provide a much tougher test than the Indonesian and Vietnamese XIs, against whom Arsenal scored seven apiece, but the Gunners had total control against Arsene Wenger's former club.
Giroud headed home from a Tomas Rosicky cross to open the scoring within three minutes, and a Tulio Tanaka handball allowed Miyaichi, playing in his home city, to thunder home from the penalty spot.
Walcott squandered several golden opportunities, but made amends on 55 minutes when Gedion Zelalem found him with an excellent through ball - the England international cut inside from the right, collected the pass and clipped the ball over the goalkeeper left-footed.
Yano headed home late on as the ball evaded Lukasz Fabianski but Grampus, who are in the middle of the J-League season, had neither the ability nor the inclination to seriously threaten a comeback.