The Japanese hosts were without five first-team regulars and fell behind in the 58th minute when Hose Mota headed home from a corner.

Gamba were quick to respond, however. Takahiro Futagawa scored three minutes later before teenager forward Takashi Usami volleyed home to clinch all three points.

The result saw Gamba climb to the top of Group H and they can ensure top spot with a win over Chinese side Henan Jianye in their final pool game later this month.

"I'm satisfied," said Gamba coach Akira Nishino. "We were in a difficult situation and I had to change the team and our playing system (to three at the back) but our players had good focus and won the game."

Suwon had already secured their place in the last 16 in their previous game but will need to beat Singapore Armed Forces and hope Gamba fail to win their last game to take top spot.

"I thought we were heading home with one point in our hand," said Suwon coach Cha Bum-kun. "But our players seemed to lose their concentration in the last part of the game."

Meanwhile, there was joy for SAF as they posted an historic first victory in the ACL by beating Henan Jianye 2-1.

Daniel Bennett put the Singapore side ahead after 65 minutes and, although Yu Le levelled for Henan shortly afterwards, substitute Erwan Gunawan grabbed the winner 13 minutes from the end.

"It is a fantastic achievement," said SAF coach Richard Bok. "I have to congratulate the team for their wonderful performance to achieve this first win for the club and for Singapore."

Opposing coach Tang Yaodong was not too disappointed with the result, admitting SAF deserved the win.

"When you create opportunities and chances but don't score, you will pay for it. That is football," he said. "Singapore football has definitely improved."