Once the bell rings, four men will play a crucial role in the bout.
Here's a quick look at the referee, and the three judges who will score the fight at ringside.
Referee Kenny Bayless
Bayless, 54, is one of the most celebrated referees in the country and has handled seven previous Pacquiao fights and five of Mayweather's. He began his career in 1993 and is heavily in demand; some years he's refereed nearly 70 fights.
He was in the ring for Mayweather's pro debut in Las Vegas, in October 1996, against Roberto Apodaca. Mayweather floored Apodaca in the first round, and Bayless stopped the fight 37 seconds into Round 2 after another Mayweather knockdown.
Bayless was also the referee in Mayweather's last fight, a unanimous decision over Marcos Maidana in September.
Bayless' seven assignments with Pacquiao date to 2006, and he most recently handled Pacquiao's unanimous-decision win over Timothy Bradley in Las Vegas in April 2014.
Getting an assignment for a big fight is nothing new for Bayless. He refereed for the Mayweather-Oscar De La Hoya fight in May 2007, which set a record for pay-per-view buys. Mayweather won by a split decision.
In his lengthy career, Bayless has handled bouts involving famous fighters in all weight classes, including Vitali Klitschko, Julio Cesar Chavez, Pernell Whitaker, Juan Manuel Marquez, Bernard Hopkins and Shane Mosley.
Judge Dave Moretti
Moretti, 70, who lives in Las Vegas, is the most prominent of the judges. He's worked nine of Mayweather's last 14 fights, and has judged six of Pacquiao's bouts.
He started judging in the late 1970s and has been involved in more than 90 world title bouts. Most assignments are in Las Vegas, but he's also handled bouts in Mexico, South America, Asia and Australia.
Moretti turned in 116-112 scores (eight rounds to four) in favor of Mayweather in three fights: against Zab Judah in 2006, Saul "Canelo" Alvarez in 2013 and in Mayweather's first fight against Maidana last year.
Moretti had scored Pacquiao comfortably ahead before his stoppages of Oscar De La Hoya in 2008 and Miguel Cotto in 2009. In Pacquiao's third fight against Marquez, in which punch statistics gave the Mexican fighter an edge, Moretti scored the bout 115-113 for Pacquiao.
Judge Burt A. Clements
Clements, 62, of Reno, has judged one Pacquiao fight, but his mistake cost the Filipino a 2004 split-decision triumph over Marquez in the first of their four fights.
Pacquiao knocked down Marquez three times in the first round, and should have earned a 10-6 score, with a point advantage for each knockdown, plus another point for winning the round. Clements admitted afterward that he didn't realize he could score a round more lopsided than 10-7. That extra point resulted in his 113-113 scorecard, which forced a draw.
Pacquiao's promoter Bob Arum dismissed Clements' Pacquiao-Marquez goof. "Here's how honorable the guy is: He admitted the mistake that night," Arum said.
Clements has been judging in Nevada since 1989. He's been assigned to three Mayweather bouts. Of the two that went the distance, Clements awarded Mayweather a dominant 120-107 score in 2009 against Marquez, and last year, Clements gave Mayweather the widest edge among the three judges, 117-111, in the first Mayweather-Maidana fight.
Judge Glenn Feldman
Of the judges, Feldman, who lives in Connecticut, is the least well known. He founded the Connecticut Boxing Hall of Fame.
He's worked only one fight featuring Mayweather or Pacquiao. That bout took place early in Mayweather's career, in 1998, against Miguel Melo in Connecticut. The fight never went to the scorecards, because Mayweather scored a technical knockout over Melo in the third round.
Feldman stays busy; this year he's already worked more than 30 fights, mostly in the Northeast.