The fist does not travel too quickly. You need to work on your reaction time, and speed. Just be faster, and react as quickly as you can.
Then I guess the planets align for me every time I spar. I've found this to be a techniques I employ about once a sparring session. Practice, repetion, and a very high degree of knowing how their telegraphing. I'm almost never caught by a surprise strike. Almost always I can tell where a punch will be. Look at my tags, they say it for me. If you are not where the strike lands, they cannot hurt you. I simply practiced, and learned how to figure out where their strike is coming from.
It isn't difficult, you merely watch their body language, and understand that based on how you are positioned, they will strike with what's vulnerable, based on that knowledge, you simply need to move from where they were intending to strike, once they begin to strike, and it is easy to place your spike right above where they had intended to hit, and then lower and retain control, or deflection.
You must use your reasoning that based upon where you were, is what they are trying to hit. But you'll need to be faster, leagues faster, than they are to pull that off. I happen to be so, naturally, because I am very small, and as I have done the arts my entire life, my physiology is adapted to utilize that speed efficiently. Just as a gymnasts body, or a horsebackriders, or even a swimmers will. It's wolff's law, and it's essential to understanding how to maximize your ability in martial arts, not only for conditioning.