Manchester United manager Sir Alex Ferguson warned his players they would have to be at their best when they host big-spending city rivals Manchester City in their top-of-the-table Premier League clash on October 23.
Champions United and City are level on points, with the latter trailing United by a single goal.
The 69-year-old Scot, who once dismissed City as the 'noisy neighbours', said he was not surprised City had made a good start to the season.
"I've said all along that would happen," Ferguson told Inside United, the club's official magazine, on Tuesday.
"They are a good team and they were always going to be there or thereabouts.
"Sergio Aguero was bound to do well, coming into the Premier League, because he is such a goal threat around the penalty box. David Silva is also a very good player.
"We just have to make sure we are ready for City when we meet them."
Both United and City have yet to lose in the Premier League this season, holding identical records of six wins and one draw, and Ferguson admitted the whole dynamic of the derby had changed since their rivals' purchase by Sheikh Mansour of Abu Dhabi.
"All derbies are big now, that is the nature of the landscape," said Ferguson.
"The impetus City now have - they have a huge squad of players and the financial power to attract some of the best footballers in the world - actually changes the focus of the derby these days.
"The talking point isn't so much the actual game but the dynamics of how Manchester City have changed football and what we do to compete with that."