Chelsea ended City's 20-match unbeaten run in all competitions with a 1-0 victory at the Etihad Stadium on Monday, with Branislav Ivanovic's first-half strike separating the sides.
That result leaves Arsenal top of the Premier League with 55 points from 24 matches, two more than City and Chelsea, who sit second and third respectively.
And Wenger does not foresee a runaway winner in the league, unlike in previous seasons.
Speaking to the club's official website, he said: "Chelsea looked always dangerous and Man City looked, for me, a bit jaded.
"They were not as fluent or as strong physically as they were at Tottenham [a 5-1 win] but it could have gone to 1-1, it could have gone 2-0 for Chelsea.
"It [the title race] is never as simple as everyone predicts. I said a long time ago that nobody will be absolutely above [the others]. It will be down to consistency."
Arsenal's own credentials are sure to be tested in the coming month with Premier League fixtures against Liverpool, Manchester United and a resurgent Sunderland to come.
And Wenger is well aware his side will need to battle to retain its place at the top and claim a first league title since 2004.
He added: "At the moment this is the period, January, February, March, where every game is a battle for everybody because everybody fights for something.
"You just want to win the games."