No one—least of all me—can accurately tell you how a fight will go before it happens, but it's definitely possible to look for patterns, storylines and tendencies.
Having watched over a dozen Pacquiao fights and at least nine from Marquez, I feel like I have a decent understanding of how the fighters respond to different situations, and how they're likely to approach their opponent in this bout.
This is my best prediction, round-by-round, of what you can expect from Pacquiao-Marquez III.
Pacquiao will enter to some classic sports tune, probably from a 1980s movie. Marquez will enter to traditional mariachi music, while wearing an enormous sombrero. He will look determined and unfazed by the occasion.
Round 1 - This will start off much like the second bout; with Pacquiao trying to quickly and explosively test his power, and Marquez trying to set the pace as more of a chess match, controlling distance and landing his counterpunches. Marquez will also be mindful of not getting knocked down early like he did in their first bout.
I expect Pacquiao to win round 1. He tends to start faster, and Marquez tends to take a round or two to get going.
Pacquiao 10 - Marquez 9
Round 2 - This is where Marquez may start to get going. Though he has improved his versatility recently, Pacquiao's best way of hitting his opponent is still an unpredictable lunging maneuver that takes an opponent getting used to. Once Marquez starts to recognize it again, "The Fighting CPA" will be able to land his trademark counterpunches to catch Pacquiao off guard, but it depends if Marquez's reflexes are still there as he goes up another six pounds, and how much speed Manny has left.
Narrow round that could go either way, depending on your judging style. I'll give it to Marquez to even things out.
Pacquiao 19 - Marquez 19
Rounds 3-6 - With both fighters hitting their prime spot in the fight, we will see a lot of the dynamic action we've come to expect when these two step into the ring together. Pacquiao will be highly energetic and throw a lot, and Marquez will do what he does best—technical counterpunching with a strong ability to throw together combinations. These rounds will be a telling indicator of how the fight will go. If either fighter sweeps these rounds, I think that fighter will be on a very positive trajectory, unless he punches himself out.
In all likelihood, I see Pacquiao winning three of these rounds, and getting an extra point for knocking down Marquez.
Pacquiao 58 - Marquez 55
Rounds 7-9 - Marquez has tremendous heart, and he'll put together a very impressive "comeback" round somewhere during this span. Pacquiao will win at least one of these rounds, and his raw athleticism will really start to serve him well here.
Each fighter takes one round convincingly, and a third is a toss-up that I'll award to Marquez.
Pacquiao 86 - Marquez 84
Round 10-11 - There will be a lot of trading at this point in the fight, and both fighters will have their moments. In all likelihood, though, Marquez will start to show his age and—like all Pacquiao opponents—will falter during these rounds. Pacquiao will be trying to pace himself and it will probably look like he is in control of the fight by now.
Pacquiao will probably take both of these rounds, unless Marquez has conditioned himself perfectly for this fight. If the conditioning program for Marquez has been effective, then he'll take one of these two rounds, and might even take both.
Pacquiao 106 - Marquez 102
Round 12 - Pacquiao will win round 12. Pacquiao has a flair for drama, and he won't want to leave anything up to chance. He'll want to put Marquez away and prove that he is the dominant fighter. I think the odds of Marquez winning this round will be very low. Pacquiao is a wellspring of energy and you know he'll put everything on the line in this round. Marquez will show a lot of heart and courage, but he will be showing a lot of wear and Pacquiao will clearly be in control of the fight.
Pacquiao 116 - Marquez 111
The Final Scorecards - My first note is that judges will have a hard time giving the fight to Marquez, even if he were to win a majority of the rounds. Pacquiao is just too popular and too much is riding on a potential showdown with Floyd Mayweather Jr. If you remember Oscar de la Hoya vs. Felix Sturm, we could be having a similar controversial situation if Marquez ends up displaying more ability than I expect him to.
That said, I believe Pacquiao will win a legitimate unanimous decision, with one judge scoring it very comfortably for Pacquiao, and one judge scoring it within three points. The third judge will be spot-on, somewhere around 116-111 for Pacquiao.
Post-Fight - The fighters will show tremendous respect for each other after three career-defining battles. There will be plenty of compliment-giving and appreciation for both fighters. If Mayweather truly wants to challenge Pacquiao, he will probably jump into the ring and do so now.