I'm not sure what mission number it is, I think it's 15, anyway It's the Rally car mission in paris in which you've catch a ford focus which is 12 seconds up in a mere 3 laps
The 206 you use is a great car for pushing hard in and you can break very late into corners with it, which was my main method for overtaking the AI. What I really like about this mission is though that I actually had to push as hard as could to beat that focus.
By the way, a word of warning when approaching the toyota corolla rally car in the first section, everytime i overtook him there he wouldn't bother braking for the following corner, seemingly just to ram into me and give the 5 second penalty