Forward David Andersen scored 15 of his 17 points in the first half as Australia took a 49-33 halftime lead.
Mills, a guard recently re-signed by the San Antonio Spurs, had 12 points in the big first half.
Wang Shipeng finished with 21 points for China, all of them from 3-pointers. He made seven of 10.
Yi Jianlian, who plays for the Washington Wizards, had a double-double (13 points, 12 rebounds) for China.