Forza Motorsport 2

You can easliy get this on the first race you enter, just go around the one time without going of the track or hitting any other cars. TIP: You can use the first lap to get in front then on the second lap race carefull.
WARNING: There is also an achievement for racing an entire race clean you can get both at one time or at different times its you choice.

You can get this achievement on any race track with any car. You just have to go around the track once and not hit any cars, drive off the track, or hit any walls. [I preferred a track that only requires 2 laps so that I could get the "Flawless Race" achievement at the same time, but the choice is up to you]