Posted by Sabrina B. @gametimegirl

In a seismic shift in the boxing business landscape, Top Rank promoter Bob Arum closed a deal with Showtime and sister network CBS to handle the pay-per-view fight between pound-for-pound king Manny Pacquiao and Shane Mosley — instead of HBO — multiple sources told ESPN.com on Friday.

Pacquiao, boxing’s biggest star, defends his welterweight title against former champ Mosley on May 7 at the MGM Grand in Las Vegas.

Pacquiao (52-3-2, 38 KOs) and Mosley (46-6-1, 39 KOs) have never fought with Showtime’s involvement and both have fought all of their numerous significant fights on HBO or HBO PPV.

While HBO spokesman Ray Stallone said he was unaware who was doing Pacquiao-Mosley, he acknowledged that Arum had informed the network that it would not be involved.

“It’s a business decision. We move on,” Stallone said.

Arum would not confirm that Showtime and CBS were handling the fight.

“Top Rank has no comment at this time,” Arum told ESPN.com through spokesman Lee Samuels.

Showtime spokesman Chris DeBlasio also said the network also had no comment.

Arum, however, has been enamored with the possibility of CBS’ involvement in the bout because of its massive reach.

According to sources, part of the deal will include CBS promoting the fight by running commercial spots advertising the pay-per-view during prime time programming. Also in the works is a series of preview shows that would run on CBS, or possibly Showtime, which would be similar to HBO’s hit reality series “24/7,” which it uses to stoke interest with weekly episodes during the month leading up to major pay-per-view fights. Pacquiao and Mosley have both had fights featured on “24/7.”

Perhaps it’s only a coincidence, but Arum recently struck a deal with Showtime to handle the production and distribution of the March 12 pay-per-view fight he is promoting between junior middleweight titlist Miguel Cotto and former titleholder Ricardo Mayorga.

Arum turned to Showtime to get involved with Cotto-Mayorga because he is angry at HBO for turning down a live network fight between Cotto, long a network staple, and 2004 U.S. Olympian Vanes Martirosyan, especially because Cotto’s fight against Yuri Foreman last summer generated the network’s highest boxing rating of the year.

Arum met with HBO Sports president Ross Greenburg for dinner earlier this week to discuss HBO’s possible involvement in Pacquiao-Mosley while he was in New York for Wednesday’s kickoff news conference to announce Cotto-Mayorga. Within the next couple of days, he closed the deal with Showtime/CBS.

At one time, Showtime was a major player in the pay-per-view boxing business. It produced and distributed several cards headlined by Mike Tyson and Julio Cesar Chavez. For many years, it held the record for the best-selling pay-per-view, nearly 2 million for the Evander Holyfield-Tyson ear bite rematch in 1997. However, Showtime has drastically cut back in recent years, doing only the occasional pay-per-view.

Despite Arum going to Showtime/CBS with Pacquiao-Mosley, he and HBO are still doing business together.

Top Rank has two “Boxing After Dark” cards booked on HBO so far this year — the Feb. 19 show headlined by bantamweight titlist Fernando Montiel against Nonito Donaire and a March 26 show headlined by featherweight titlist Yuriorkis Gamboa against Jorge Solis.

Dan Rafael covers boxing for ESPN.com. Follow him on Twitter.