A 3-0 home victory last week has put Gamba firmly in the driving seat but manager Akira Nishino has ordered his players to go for the win in the return match.
"We are certainly not going there with the mindset that we can afford to let them score two goals," Nishino told reporters before the team left Japan for Australia.
"With the atmosphere here there is a lot of pressure but we'll put the (three-goal) advantage out of our minds. We plan to win the game."
Gamba dominated last week's first leg and were unlucky not to have scored five or six goals. Japan midfielder Yasuhito Endo, Brazilian Lucas and and Michihiro Yasuda were on target in a one-sided game in Osaka.
"We should have killed it off with a fourth goal," said Nishino. "But we stopped them from scoring an away goal which was important."
A first Asian Champions League title would give Nishino's side a spot in December's lucrative FIFA Club World Cup in Japan, involving European champions Manchester United among others.
Adelaide have already qualified for the tournament as the highest-placed non-Japanese side.
Favourites Gamba knocked out champions Urawa Reds 4-2 on aggregate in the semi-finals. Urawa broke a miserable run for Japanese clubs in the competition with their 2007 triumph.
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