Gamba were too organised and skilful for the inexperienced Reds team.
Gamba, the last Japanese club to lift the trophy with their final victory over Adelaide in 2008, were too organised and skilful for the inexperienced Reds team.
Tall striker Shun Nagasawa put the J-League outfit ahead with a powerful header off Oh Jae-Suk's curling cross in the 21st minute.
Midfielder Yasuyuki Konno rammed home a rebound in first-half stoppage time to put Gamba in command of the away tie.
Gamba rounded off the scoring when their skipper Yasuhito Endo's free kick was put into the Reds' net by defender Dylan McGowan for an own goal with nine minutes left.
Endo, who bossed the midfield, whipped in his free kick from the right, eluding Reds goalkeeper John Hall, and it deflected off McGowan into the unguarded net.
It was Gamba's fourth win over Adelaide in six meetings and a boost to their chances of reaching the knockout stages of the Asian showpiece tournament.
Gamba Osaka will be at home to South Korea's Jeju United in their next ACL match, while Adelaide travel to Jiangsu Suning in China on March 1.
In Group G, Kawasaki Frontale were held to a 1-1 home draw by South Korea's Suwon Samsung Bluewings when Shogo Taniguchi's own goal cancelled out Yu Kobayashi's 11th-minute opener.