There was such concern from the Canelo Alvarez camp about whether Julio Cesar Chavez Jr. would make weight for their heavily anticipated fight on Saturday night in Las Vegas that their contract stipulated the fighters hold a secret weigh-in to determine any possible financial penalties minutes before the Nevada State Athletic Commission's official weigh-in, multiple sources with knowledge of the situation told ESPN.com on Tuesday.

Chavez, the bigger man and notorious for missing weight for a number of previous bouts, agreed to fight the smaller Alvarez at a catchweight of 164.5 pounds, 9.5 pounds heavier than Alvarez had ever fought at and the lightest Chavez had agreed to fight at since losing his middleweight belt to then-lineal champion Sergio Martinez in 2012.

The Alvarez-Chavez contract called for both fighters to be penalized for anything over 164.5 pounds, at a cost of $1 million up to 165.6 pounds, at which point the penalty would be $2 million. Nobody was concerned about whether Alvarez would make weight, but both camps had serious concerns about whether Chavez would make it.

Concern from Canelo Alvarez's camp about Julio Cesar Chavez Jr.'s ability to make weight for their highly anticipated bout led to a contract stipulation that the fighters hold a secret weigh-in minutes before the official weigh-in, sources told ESPN. Joe Camporeale-USA TODAY Sports

So on Friday afternoon, in one of the salons downstairs at the MGM Grand Garden Arena, members of both camps gathered while an expert calibrated a digital scale. The contract called for a digital scale to be used, as opposed to the less precise deadweight scale used by the commission, sources said.

Then, about 10 minutes before the official commission weigh-in, came the secret weigh-in, which was overseen by retired federal judge Daniel Weinstein, one of the nation's preeminent mediators. He was involved in helping get Alvarez promoter Golden Boy Promotions and Chavez adviser Al Haymon -- bitter enemies-- to finalize the deal for the fight. Weinstein also mediated the eventual settlement between Golden Boy and Top Rank over Manny Pacquiao's promotional contract in 2007.

According to sources, besides Weinstein and the fighters, others at the secret weigh-in included Alvarez trainers Eddie and Chepo Reynoso, Golden Boy president Eric Gomez, Golden Boy chief operating officer Robert Gasparri, Golden Boy matchmaker Robert Diaz, Golden Boy attorney Ricardo Cestero, Haymon, Julio Cesar Chavez Sr., Chavez trainer Ignacio "Nacho" Beristain and TGB Promotions CEO Tom Brown, who served as Chavez's promoter for the bout.

As much concern as there was over Chavez's weight, he actually weighed in lighter than Alvarez. Sources said Chavez was 163.6 pounds on the digital scale and Alvarez was 163.8 pounds.

Minutes later, Alvarez and Chavez -- with a smile on his face knowing he had made weight as it pertained to any potential financial penalties -- came to the deadweight scale in front of thousands of fans and the media contingent inside the MGM Grand Garden Arena. Both fighters weighed in at 164 pounds.

The next night, in perhaps the biggest all-Mexican rivalry fight in boxing history, Alvarez (49-1-1, 34 KOs) routed Chavez (50-3-1, 32 KOs) in a shutout decision, 120-108 on all three scorecards, before a sold-out crowd of 20,510 at the T-Mobile Arena.