When Japan attacked the Western Allies in 1941, Sakai participated in the attack on the Philippines as a member of the Tainan Air Group. On 8 December 1941, Sakai flew one of 45 Zeros from the Tainan Kōkūtai (a Kōkūtai was an Air Group) that attacked Clark Air Base in the Philippines. In his first combat against Americans, he shot down a Curtiss P-40 Warhawk and destroyed two B-17 Flying Fortresses by strafing them on the ground. Sakai flew missions the next day during heavy weather.