Easy when boosting online. Start a career multiplayer match with 2 players, both identical riders. Make it all the way around the track and wait 5- 10 meters before the finish line. Dont get penalties for going off track!!!!
Now let the player going for the achievement stand about the length of a tire ahead of the other. Then accelerate at the same time and if you finish with less than 0.1 seconds ahead of the other player, you will earn the achievement.