For this achievement you can win against AIAs this one only requires you to win an online game the fastest method is to do a 1/8 mile drag race against AI.
To create a game:
-Community
-Race Online
-Create Race
-Game setup
-Game Type - Drag
-Track - Sedona Drag 1/8
-Max Players - 2
-Max AI Players - 1
-Car Class - Any
Then select your car the
1973 Porsche 911 Carrera RS and change the AI car to something slow.
Start the race and win for the achievement.
Here's a video, you do not have to own the car.