Competing for the second time in a calendar year for the first time since 2007, Mayweather looked sharper and more majestic than in his last several fights as the previously-unbeaten Alvarez looked to become the first man to 'crack the code' of the incomparable American.
Though Canelo surprised his foe with his early sharpness, leading to Mayweather's father and cornerman Floyd Snr to urge him to relax, relax was exactly what 'Money' did from there as he began to frustrate the Mexican with his uncanny ability to switch gears and pick off crisp shots as he pleased.
Whenever Alvarez was able to dig deep and find a new approach to the fight, Mayweather would have an answer in another masterclass in top level boxing against a top opponent.
Alvarez matched Mayweather's 152lb catchweight at the weigh-in, but entered the ring at around 165lbs with Mayweather saying after the fight that he woke up Saturday morning at around 147 before scaling just before bell-time at 150.
Hoping his size advantage would help him find the power punch finish, Alvarez started tentatively, giving the Michigan man a taste of his own medicine with some snap counter-shots.
Once Mayweather came to terms with his opponent's refusal to play into his hands, his superior conditioning and multi-faceted ring generalship soon underscored the gap in quality.
Alvarez began to overcome his own frustration in the latter rounds, and admitted as such after the fight, and though he was able to impress in a couple of rounds with sheer resolve and work rate, he did not come close enough to finding the stoppage he now needed if he were to stay unblemished.
While a more open fight than the usual Mayweather clinic, there was still surprise to be had when the decision came back as majority, not unanimous.
CJ Ross, who scored the Manny Pacquiao v Timothy Bradley bout last June in favour of the outmatched American to much controversy, somehow regarded Mayweather-Alvarez as a draw.
Craig Metcalfe and Dave Moretti meanwhile offered 116-112 and 117-111 in favour of Mayweather, who now adds Alvarez's WBA regular and WBC belts to his WBA 'Super' title won in the 2012 Miguel Cotto fight.
The Eurosport-Yahoo! scorecard also had it 117-111 for Mayweather, with one of Canelo's three rounds admittedly being a final round which the American spent ensuring he did not get close enough to a potential dramatic late knockout.
"I just listened to my corner, listened to my dad," Mayweather said. "My dad had a brilliant game plan, and I went out there and got the job done."
"I didn't know how to get him, it's extremely simple," Alvarez explained. "He's a great fighter, very intelligent. The frustration was getting in there, but he's a great fighter. We tried to catch him."