Highlights - Netherlands 1-0 Japan
Netherlands coach Bert van Marwijk said there was more to come from his side as they become the first team to reach the last 16 at the 2010 World Cup.
Wesley Sneijder's winner against Japan, coupled with Denmark's win over Cameroon put the Netherlands through.
"Everyone could see Japan do not have a bad team," said van Marwijk in Durban. "And then you have to be very patient.
"We can do much better, but with six points from two games without conceding you can't say you're not satisfied."
"We came here to win a prize, to become world champions," he added after the Dutch extended their unbeaten run to 21 matches.
"That's far from straightforward and easy. [But] if we can continue to show stability, and if we maintain confidence in really winning something, we might get far. So the target is to go for the prize.
You have to be able to win ugly games
Dutch coach Bert van Marwijk
"Let me assure you that we really, really want to win and if we can do that in style then great. But you have to be able to win ugly games."
The Netherlands laboured to a 2-0 win over Denmark in their opening game in South Africa but they lead the group with six points from two games.
The Dutch need just a point from their group game against Cameroon on Thursday to guarantee top spot.
"What you need is a bit of luck," added Sneijder, whose 52-minute shot was deflected into the goal by Japan keeper Eiji Kawashima when he was well positioned to save it.
"We ended up at 1-0 and I think, at the end of the match, we should have ended up with 2-0 or 3-0."
Despite Sneijder's comments, Japan did come close to snatching a late equaliser as unmarked substitute Shinji Okazaki fired over the bar before referee Hector Baldassi waved away penalty claims when Yuto Nagatomo went down under a challenge from Nigel de Jong.
And coach Van Marwijk recognised how close they came.
"It shows you there are no easy games. Look at France and Germany," the Dutch coach reflected.
Having said they would wait until the morning of the game before deciding whether to risk Arjen Robben, the Netherlands decided not to bring the Bayern Munich winger off the bench against Japan.
Robben completed a full training session on Friday for the first time since injuring his hamstring in a warm-up match against Hungary on 5 June.