Roberto Mancini's men are currently two points clear of their city rivals.
City travel to Old Trafford as part of Sky Sports' Super Sunday, and De Jong has victory firmly in his sights.
"Of course everyone believes we can go there and win. We're going there as number one and the aim is to stay number one," he said.
"We are on top of the league so going into that game we just have to be confident and play our game as well as we have been doing.
"The pressure is still the same as it was last year. But what has changed is that we are now number one going into this derby.
"We don't have any point to prove. We've shown our quality throughout the season. We don't need a game against United to show how good we are.
"But it's two of the best teams in England going up against each other and I expect it to be a great game.
"Everyone was talking about that FA Cup semi-final but we proved we can win. Now we have to go into this game believing we can get the three points."
De Jong feels City's last-gasp Champions League win over Villarreal on Tuesday night was timely.
"It's a big boost for us," he said.
"Every game you win gives you something extra going into the next game. That's especially the case when you've got a game like this one on Sunday.
"The belief has always been there for us. We're confident but United will be as well. They're at home and it's a massive game for both of us."
De Jong also insists that City are starting to build a history, after ending their trophy drought last season by winning the FA Cup.
"You can't build a history of winning trophies over 25 years like United have done just in one year," he said.
"There's more to come but we are building here step by step and that takes time. Maybe you don't get a lot of time when you are spending a lot of money on players. But still you need to go step by step - that's how it has to be.
"The other side is that everyone is hungry for success and it has to come as quickly as possible for most of us."