The game in Japan ended 5-3 in United's favour and they will now meet Liga Deportiva Universitaria Quito of Ecuador, in the final on Sunday.
"Gamba really played well, I was impressed," Fergie said after the game.
"They have a talented team and proved that Japanese football is getting better and better.
"Gamba surprised us with their formation and caused us a few problems until we adapted a bit better to them.
"The fans got their money's worth today.
"It was a great match and the score could have been even higher. Edwin van der Sar made a couple of saves and we also had countless opportunities that we couldn't convert."
"I'm very pleased that we've made it to the final, but we will be facing a stern test, as Liga de Quito are very strong defensively. It's never easy against South American teams."