Very easy to get.
Hit up Free play and choose the 2017 Ford GT from your cars. If you don't have it yet for the other achievement for owning it, you can rent it.
Choose Homestead - Speedway Circuit as your track and then go to your game options and set your Max Drivatars to 23 for a full field, drivatar difficulty to New Racer or whatever difficulty you are comfortable with beating them, set laps to 1 and collisions to off.
Once you start the race, you will start near the mid/front and with collisions turned off, you can drive right through the field into first. I did it very easily with just Average drivatar difficulty and on Homestead you can finish the lap between 30-35 seconds.
Achievement pops when you finish in first.