Upload & Sell: Off
This isn't too difficult to do once you get used to it. Probably you need to get a couple of core principles nailed down that might run in total contradiction to what you need for your usual work.
First, use what in Canon world we call AI-Servo, meaning that if the button (shutter or AF-on/*) is being pushed, the camera focuses. They are moving towards, which even at fifty-five minute 10K speed means that the runner has moved six inches to a foot in the time you take to drop the AF and then hit the shutter. They're forward progress is a dream for modern AF systems because the speed is not going to change much which is great for the predictive algorithms.
Second, pick a single focus point, most likely the centre spot, which usually has the most sensitivity. You may need to dial in the AF tracking speed (I've got my Canon 1Diii set on slow).
Third, keep the point on the runner's number -- the high contrast between the white background and the dark of the number is heaven for an AF system.
Fourth, shoot a bit loose if you are on the finish line in case folk put their arms up in victory.
The specifics of the D4 AF system will probably mean you need a change in some of the details (I'll have to figure this out with the Dx soon, I hope), but the basics of the technique stay the same. It should let you keep shooting wide open, which is what will likely set you apart from some of the others crowing the finish line.
One other thing I would point out is that most people look like they're ready to drop dead on the finish line, which is why I usually take the shot twenty to thirty metres before the line when folk are still hammering and have a look of anticipation on their face. Yup, I miss some finish line jubo, but I get far fewer shots of people looking like they need medical attention (including those who all but fall on me).