Substitute James Troisi's extra-time goal gave the Socceroos a 2-1 victory at the Stadium Australia in Sydney on Saturday – sealing the hosts' first Asian Cup title.
And Swansea City midfielder Ki was quick to praise Ange Postecoglou's side.
"I think they were the better team, we had a chance to win but in the game they were better than us with the ball and really well organised," said the South Korea captain.
"They had more strength in extra time and they have some young players – some really good young players as well.
"Australian football has come a long way since I was here last, it has changed so much, it is not just long ball.
"They are now really comfortable on the ball, and the team has a very good manager and they deserve to be the champions."
Massimo Luongo put the hosts in front during a captivating first half, but his excellent strike was cancelled out by Son Heung-min in second-half stoppage time.
But Uli Stielike's side were unable to build on their late comeback, and Troisi stole in to convert the winner in extra time.
Skipper Ki believes South Korea have work to do in order to become the best side in Asia.
"I think we played better today than we have done so far in the tournament and I thought when we scored so late we could go on and win, but we weren't strong enough," he added.
"We had injuries, so we had to replace experience with younger players.
"It's good for them to get the experience, but we now have to learn to become a stronger and fitter team to get to be the best again."
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