Wales would go to Japan with a lot of belief and self-confidence, he said.
Gatland was disappointed with their loss to Ireland on Saturday but Wales had shown great character in the second half, looked fit and began to play with real purpose. They could have gone on to win the game, he said.
Wales would pick a strong side for their return game with Ireland at the weekend.
"Ironically, if we can win next week, it almost reflects what happened in 2011 in the warm-up games. We'll be going over there having had a good week and I'll be picking a pretty strong side," he said.
Gatland repeated the comments of many other observers when saying the World Cup was as open as it had been for a long time.
"The All Blacks losing in Perth was a shock but they just showed what they can do the following week when their minds are on it.
"South Africa are improving all the time.
"There are six or seven teams capable of winning the World Cup. You always need a little bit of luck. You get to the quarterfinals and then take it one game at a time.
"We go there with a lot of confidence. England will be tough out there, they have a huge side. They'll have a very good chance," he said.
Gatland has gone for an 18-13 split in his selection and he said if there was one area they were a little light it was in their propping. He has gone with five props instead of six.
"When we decided to go with the five props, one of the big discussion points was how durable they are," he said.
"The most difficult thing about this squad is the depth we've created over the last three or four years, so we've left out some real quality players.
"In the past when you've picked a World Cup squad, you may have been happy with 24 or 25 players and the others making up the numbers, you're not sure about their quality.
"But this time we've left out some class players," he said.
Wales were in great physical condition, and there had been comments in the second half against Ireland how strong they were looking.
"We still have a few weeks to help us prepare. I think the northern hemisphere sides have got a great chance of doing well in this World Cup," he said.