As the old saying goes, as one door closes, another one opens.

Oscar De La Hoya's Golden Boy Promotions stable of fighters, including Canelo Alvarez, the unified middleweight world champion and boxing's biggest superstar, have long been stalwarts of HBO. But with the premium cable network's recent announcement that after 45 years of putting on most of the biggest fights in boxing it was bowing out of the sport at the end of the year, they were in need of a new broadcast home -- and they have landed a very lucrative one with new sports streaming service DAZN through 2023.

In a record-shattering deal finalized early Wednesday morning, Alvarez signed a five-year, 11-fight deal worth a minimum of $365 million with DAZN, which only launched in the United States in September.

It will commence with his move up to super middleweight to challenge secondary world titlist Rocky Fielding on Dec. 15 at Madison Square Garden in New York, where they will meet face-to-face at the kickoff news conference on Wednesday afternoon.

Alvarez's deal is the richest athlete contract in sports history, eclipsing the 13-year, $325 million agreement that New York Yankees slugger Giancarlo Stanton signed in 2014 when he was with the Miami Marlins.

"Canelo is the highest-paid athlete in the world. He's extremely happy," De La Hoya told ESPN after Alvarez signed.

HBO had the right of first negotiation and a last-look provision for Alvarez's fight with England's Fielding (27-1, 15 KOs), and the network made an offer for an HBO PPV event, but it elected not to match the one made by DAZN.

Although rumors that the deal was imminent have swirled for a few days, it was not finalized until after 1 a.m. ET Wednesday, when Alvarez, accompanied by manager Chepo Reynoso and trainer Eddy Reynoso, signed the contract following a lengthy meeting with De La Hoya and Golden Boy Promotions president Eric Gomez at a hotel in New York's Times Square.

Alvarez is boxing's biggest pay-per-view star of the post Floyd Mayweather/Manny Pacquiao era, generating hundreds of millions of dollars for events on HBO PPV and, before that, Showtime PPV. But the move to DAZN will take him off HBO PPV -- where his fights cost around $80 apiece for viewers -- and place his two fights per year on the all-sports streaming service that charges $9.99 a month for a slew of combat sports offerings.

When Alvarez was fighting on pay-per-view, he would earn money for every buy above a set threshold beyond his guaranteed purse. But even though DAZN doesn't offer pay-per-view, Alvarez can still earn even more money beyond his guarantee based on specific subscription benchmarks that DAZN can reach during the course of the deal.

Canelo Alvarez, right, signs his record DAZN deal with Oscar De La Hoya of Golden Boy Promotions. Courtesy of Oscar De La Hoya

"This is only from my hard work," Alvarez told ESPN shortly after he signed the paperwork. "The most important thing to me was being able to give the fans the opportunity to see me fight without having to pay the $70 or $80 for my fights on pay-per-view. That was the most important thing, more important than what I am making.

"It's very important for me to give the fans the biggest fights and the most important fights, and I promise you I will always do that. The December fight with Fielding is a dangerous fight. I am moving up in weight, and I don't know how my body will feel. But I always want to take on challenges, and I am very happy my fans will be able to see me fight for a small cost."

Alvarez said he was not worried that he was moving to an unproven broadcast platform.

"Never. I was never worried because I'm very confident in myself," he said. "I know how important I am to any platform I go to. I am very grateful to HBO and to Showtime for what they did for my career, but I am happy we're moving forward and that I will be able to fight on a platform that is the future. I've always liked a challenge, and this is yet another challenger in my career.

"Being part of this historic deal will require me to prepare myself even more and offer fans even better performances. At the same time, I am humbled to be selected to lead this new vision for the sport of boxing, which will without a doubt be for the benefit of the fans."

Although Alvarez is the centerpiece of the deal, De La Hoya had leverage to use Alvarez to secure dates and license fees from DAZN for his company's non-Alvarez events. The deal, for which financial terms were not disclosed, calls for Golden Boy to put on up to 10 "high-caliber fight nights" per year that will stream live on DAZN beginning in early 2019.

Those fights would include Golden Boy's other top fighters, including junior welterweight and former three-division world titlist Jorge Linares, junior featherweight titlist Rey Vargas, middleweight contender David Lemieux, featherweight contender Joseph Diaz Jr. and junior featherweight contender Diego De La Hoya, as well as junior lightweight Ryan Garcia and junior welterweight Vergil Ortiz Jr., two of boxing's top prospects.

"This is huge for boxing, huge for Canelo and huge for Golden Boy," De La Hoya said. "Golden Boy is at the forefront of something very monumental for the sport of boxing."

Because of how well the pay-per-view sold, Alvarez (50-1-2, 34 KOs), 28, of Mexico, earned around $50 million for his rematch with Gennady Golovkin, whom he outpointed to win the unified middleweight title on Sept. 15 in the year's biggest fight. Now, Alvarez will get a fee from well-funded DAZN for his events as the streaming service tries to make inroads in the United States after previously launching in Japan, Italy, Germany, Austria, Switzerland and Canada, where the Golden Boy and Alvarez fights also will be included with subscriptions.

"This is easily one of the best days in the growing history of Golden Boy Promotions," De La Hoya said. "We are committed to making this sport as accessible as possible and at an affordable price for all the fans. My dream has been to make boxing a sport for all. DAZN has the perfect platform to make this dream come true, and with the biggest star in the sport at the helm of this journey, I have no doubts that we will succeed in unimaginable ways."

When HBO announced in late September that it would cease televising boxing, De La Hoya and Gomez immediately began looking for a new home. They talked to ESPN, Turner and Showtime, with which they once had a deal and where Alvarez had his biggest pay-per-view fight (a 2013 loss to Mayweather).

But about two weeks ago, De La Hoya and Gomez also met with John Skipper, the executive chairman of Perform Group, DAZN's parent company, in Los Angeles. De La Hoya and Skipper already knew each other from when Skipper was the president of ESPN and Golden Boy had a limited deal for a series of boxing events on the network; and they were able to make this deal in relatively short order because De La Hoya needed a home for his fighters and Skipper, with money to spend, needed content for the new service.

"We were able to reach a conclusion of what Canelo is worth today and what he is worth tomorrow, and we worked out this deal," De La Hoya said.

Said Skipper: "We are thrilled to be exclusive partners with Golden Boy Promotions and Oscar De La Hoya. By bringing Canelo's fights to DAZN, we will turn his pay-per-view success into a growth engine for subscribers -- a truly transformational moment for our business and the entire industry."

By signing Alvarez, DAZN now is the home for boxing's two most significant superstars, as it also is the American broadcast location for unified heavyweight world titleholder and British fighter Anthony Joshua. Joshua's promoter, Eddie Hearn of Matchroom Boxing, signed an eight-year, $1 billion deal with DAZN in May to deliver 16 events annually in the United States, along with the 16 per year he already was putting on the United Kingdom. That deal kicked off Sept. 22 with Joshua's title defense against Alexander Povetkin.

The deal with Golden Boy also will give DAZN access to the roughly 7,000-hour library of Golden Boy's fights, including from De La Hoya's Hall of Fame career. Golden Boy Media and Entertainment also will produce various shoulder programs to complement the live events.

DAZN, whose other boxing property is the World Boxing Super Series and its three second-season tournaments, is the latest entrant into a crowded boxing broadcasting field, even as HBO winds down its historic run.

ESPN and Top Rank recently tore up a four-year deal made in 2017 and entered into a new seven-year agreement that runs until August 2025 and calls for 54 live boxing events annually between ESPN and ESPN+. Al Haymon's Premier Boxing Champions recently completed a four-year rights deal with Fox that begins in December, and it also finalized a new three-year deal with longtime partner Showtime.