Juan Estrada defeated Roman "Chocolatito" Gonzalez via split-decision to unify the junior bantamweight division.
Judges scored the contest 117-111, 115-113 and 113-115 in favour of Estrada, who avenged his 2012 unanimous decision defeat to Chocolatito in 2012.
In doing so, Estrada added the WBA title to his WBC and Ring Magazine titles to establish himself as the best fighter at 115-pounds. The fight was a spectacle for fans in attendance with a record 2,529 punches thrown between them.
Despite being in March, it is already the Fight of the Year and while Srisaket Sor Rungvisai is mandatory challenger for Estrada, a trilogy between the pair could come into fruition instead.
The 117-111 score in favour of the Mexican drew criticism though, with many believing Gonzalez had done enough to edge it.
Reaction - "Greatest fight I have ever watched live"
"I think I did enough to deserve to win," said Estrada, who finished with a career-high 1,212 punches.
Estrada, 30, added: "[He] is a great fighter and I think he deserves a trilogy.
"I knew it was a close fight. I didn't know if I was up or down, but I knew I had to close out the fight in the last two rounds."
Gonzalez - a four-division world champion - is hopeful of a third installment.
"Whatever happened, happened, but I gave it a great fight. I would have been happy either way with the result. I did my work," Gonzalez said through an interpreter.
"It was a better fight than the first one. I felt I won. In the last round, I gave it all, it was a great round. I'm happy because I'm going back home to see my family.
"I won both of them. Whatever Estrada wants, we'll do it. I'm very happy with my performance and having the crowd enjoy the fight."
Promoter Eddie Hearn claimed it was "the greatest fight I have ever watched live" and wants to make the third fight.
Repeat for McCaskill, Taylor next?
Jessica McCaskill made a successful first defence as undisputed welterweight champion, defeating Cecilia Braekhus via unanimous decision.
The American, who beat Braekhus in 2019, overcame the legend with wide scorecards of 100-89, 99-90 and 98-91.
McCaskill - who now has a 10-2 record - could potentially rematch Katie Taylor, who defeated her in 2017 if the Irish star decides to move up from lightweight. Undefeated Taylor could have the chance to become undisputed champion in a second division if so.
Elsewhere, Hiroto Kyoguchi retained his WBA junior flyweight title, stopping Axel Aragon inside four rounds to make a third successful defence of the strap he won in 2018.