Get into as many car's slipstreams as you can. When you're into the first corner overtake as many cars as you can from the inside (off the bank if you have too), I think I overtook 4. As soon as you're onto the straight get into the car's slipstreams again, dive out to overtake and immediately get back into a slipstream again. Expect to do this several times... but if you've done it well you should only have 2 cars in front of you by the end of the straight. Get into the 2nd place car's slipstream in mid-second corner, and you should be able to overtake it on the inside half way through the corner. From then on you should have gained enough speed to beat the first place car by at least 1.5 seconds.
And yes, I done this will all aids off, Pro, Manual