At the start of the month, the Red Devils went eight points clear of their local rivals following a 2-0 victory over Queens Park Rangers at Old Trafford.
With the teams still to play each other at the Etihad next week, United's slip has let City right back into the title race, with Roberto Mancini's charges now just three points adrift.
"United's result was amazing," Toure told Sky Sports News. "It was an unbelievable day for us with United dropping points at home. For me, it was strange. We found out about it on the bus on the way to Wolves. It was quite unbelievable and we now have to try and take advantage.
"When your big rivals drop points at home, and you have to win your game, it is quite difficult. But with the players we have, it can make the difference all of the time with the likes of Aguero, Tevez and Nasri, and we did the job.
"We did the first part by beating Wolves but we have to settle down and continue to work hard because United still have three points more than us. We have to play them at home and, if you look at the record of United, they are very strong away and it will be a very difficult test for us."
Toure moved to Manchester City from Barcelona in 2010.