This is less about English than racing terminology. It helps if you understand drag (friction caused by the flow of air around the car) and how drafting (riding closely behind another car) reduces this drag.
"First" in this case refers to "First Place". If you draft behind the lead car you can use the temporary reduced drag to slip around at the last moment and "slide" into first place, winning the race. Apparently this is fairly complicated in the real world (not to mention dangerous) but in an arcade game the real-world aerodynamics are simplified to make the game more enjoyable.