Lucas Matthysse, the big slugger from Argentina, and Viktor Postol, a technical boxer from Ukraine, will square off for a vacant junior welterweight world title Oct. 3 at the StubHub Center in Carson, California, after their promoters agreed to a deal for the mandatory fight Monday.

"There's a deal in place, and we have the arena reserved. It's going to be a great fight," Golden Boy Promotions president Oscar De La Hoya told ESPN.com after cutting a deal with Top Rank, which co-promotes Postol with Ukraine's Elite Promotions. "The way I see it, any Lucas Matthysse fight ... always calls for action. We've seen him in wars. We don't know much about Postol. The United States hasn't seen him in wars, but come Oct. 3, people are going to know Postol and know he is a strong fighter."

The camps made a deal just in time to avoid a WBC purse bid scheduled for Monday in San Diego. They had been close to a deal for the past couple of weeks so they requested, and were granted, a one-week extension on the purse deadline last week.

Lucas Matthysse, above, and Viktor Postol will be fighting for the 140-pound world title that Danny Garcia recently vacated. Emily Harney/Hoganphotos/Golden Boy

"It's a really interesting fight, style-wise," said Top Rank vice president Carl Moretti, who negotiated the deal with Golden Boy's Eric Gomez. "You have a long, tall, strong fighter in Postol, who would give any 140-pounder problems. And Matthysse is clearly one of the top 140-pounders in the world. Just because Postol isn't well known doesn't mean he isn't one of the top 140-pounders as well."

The fight will headline an HBO-televised doubleheader, although De La Hoya said he is still in the process of finalizing the deal with the network.

"We're working through it, but it will get done," De La Hoya said.

De La Hoya said the co-feature will be another junior welterweight bout, this one matching hot prospect Antonio Orozco and veteran contender Humberto Soto, a former junior lightweight and lightweight world titleholder.

The 5-foot-6 Matthysse and 5-11 Postol will be fighting for the 140-pound world title that Danny Garcia recently vacated in order to move up to welterweight, where he will face former titleholder Paulie Malignaggi on Aug. 1 (ESPN).

Garcia had been ordered to face Postol in a mandatory defense but made a deal with him to step aside so he could face Lamont Peterson in April while Postol appeared on the undercard and won an eight-round decision against journeyman Jake Giuriceo to stay sharp for the title fight.

When Garcia vacated -- because he would have been stripped since he was not going to fight Postol -- Postol was ordered to face Matthysse, the next leading available contender.

Matthysse (37-3, 34 KOs), 32, one of boxing's most fearsome punchers and most exciting fighters, is coming off a majority decision win against former titleholder Ruslan Provodnikov on April 18 in an HBO main event that is, so far, the clear-cut 2015 fight of the year.

The 31-year-old Postol (27-0, 11 KOs) made his HBO debut in May 2014 at the Forum in Inglewood, California, and scored a sensational 11th-round knockout of longtime contender Selcuk Aydin in a title elimination bout that made him the mandatory challenger.

"It was a great knockout and it shows you that Postol has the ability to do that, and Matthysse isn't the hardest guy in the world to hit, so it should be interesting," Moretti said.

Added De La Hoya, "It calls for an entertaining fight, a fight with a lot of action. This is the perfect fight at the perfect venue. Matthysse is exciting. He's a power puncher. So it should be a dangerous fight for both guys, which is what Golden Boy is all about.

"I know Postol is a strong fighter, but at the same time, he has that long reach and that long jab, which makes him dangerous. It's going to be up to Matthysse to break him down, figure him out and make the fight work in his favor."

Orozco (22-0, 15 KOs), 27, a native of Mexico living in San Diego, will be taking on the most notable opponent of his seven-year pro career.

He has a penchant for being in hard-hitting fights, as does Soto (65-8-2, 35 KOs), 35, of Mexico, who finally has a fight scheduled after two others fell apart in recent months. He was supposed to face prospect Frankie Gomez on the Canelo Alvarez-James Kirkland undercard May 9 at Minute Maid Park in Houston, but the fight was canceled because Gomez was 6½ pounds overweight at the weigh-in the day before the fight.

Soto was quickly rescheduled to face former two-time lightweight title challenger Raymundo Beltran on June 27, but when Beltran tested positive for a performance-enhancing drug, the fight was canceled. Soto was lined up to face replacement Jose Felix Jr., but on the day the fight was made, Soto suffered a knee injury while running.

De La Hoya said Soto's knee is healed and that he will be prepared for Orozco.

"He's had a couple of bad-luck situations recently, but he's motivated and ready to go," De La Hoya said. "We feel Orozco is ready for this kind of fight. We feel this is the perfect step for him. It's dangerous fight for both guys, but it's a great fight for the fans."