I have yet to see Pac or Roach correct this mistake. Once Pac comes in, he's already committed. He needs to learn how to counter on top of his opponents counter. Set them up with a jab, maybe double on it, wait for their 1-2 counter then unload....rather than just charge in, throw his combo and then get clocked.
That's all Marquez was doing. Let Pac throw his combos, once that left hand is launched Pac doesn't do a good job covering up for the counter, if anything there have been plenty of times that Pac will follow with that left and just stand there.