The pound-for-pound lynchpin suffered his first knockout loss since 1999 in devastating fashion as Marquez landed a perfect overhand right that sent Pacquiao straight to the canvas.
Coming into the fight, there were plenty of questions surrounding the high-profile boxer. Everything from his motivation to cardio have been the center of speculation leading up to this fight and we got to see some of those questions answered on Saturday.
Looking back on the epic fourth fight with Marquez, here are three things that we learned about Pac-Man.
He's Still Motivated
Much has been made about Pacquiao's approach to the sport lately. His celebrity status and political career spark a lot of conversation about whether or not he still has the competitive fire to compete with the world's best in boxing.
Despite the loss, the answer to that question is yes.
There was a point in the fight that it looked like the resounding answer was no. In Round 3 Marquez landed a huge overhand right that caught Pacquiao flush on the chin and knocked him down. While Pac-Man shook off the knockdown physically, it appeared he might not have mentally.
For the next few minutes, Pacquiao seemed to be hesitant and withdrawn. The critics appeared to be correct.
Then he came out in Round 4 and seized back control of the fight. By Round 5 it looked like he was back in control as he used his legendary straight left to put Marquez down and finished with flurry after flurry trying to put Marquez away.
He was even winning Round 6 before the counter punch that knocked him out connected.
You can say that Pacquiao lost because he opened himself up to a counter, but you can't say it was from lack of motivation.
He Still Has Power
Anyone wondering if Pacquiao still packs a punch got their answer on Saturday. His power was on full display.
Pac-Man was able to land his power shots throughout the fight and used them to build up an advantage on the scorecards. When he landed the big straight left to knock Marquez down in the fifth then proceeded to get aggressive to end the round, he looked like vintage Pacquiao.
Marquez was able to survive long enough to land the overhand right that ended the fight, but if he hadn't landed one massive counter, the fight appeared to be heading in the opposite direction.
He's No Longer Vintage Pacquiao
Pacquiao has had a great career.
He'll go down in history as one of the greatest fighters of his era and an undeniably great champion. Few have possessed the combination of power and aggression that he has displayed in numerous weight classes over the course of their careers like he has.
However, the days of him being an unbeatable behemoth are over.
Will Pacquiao bounce back?
There's an argument to be made that those days were over in Round 3 when Marquez put Pacquiao down with a power punch of his own. In their three previous fights, you would have never seen Marquez floor Pacquiao in that fashion.
When Marquez sealed victory in the Round 6, it was official. Pacquiao no longer has a case as a top pound-for-pound fighter in the sport today.
The loss for Pac-Man makes two in a row. While it's still tough to count a questionable decision loss to Timothy Bradley against him, this one had much more finality to it.
The "old" Pacquiao is long gone.