Fights involving a pair of boxers on the rise and two veterans seeking a notable win to push them closer to another title shot will highlight the undercard of the welterweight unification fight between Errol Spence Jr. and Shawn Porter.

Junior welterweight up-and-comers Mario Barrios and Batyr Akhmedov will meet for a vacant secondary junior welterweight world title, and welterweights Josesito Lopez and John Molina Jr. will square off in a 10-round fight, with Premier Boxing Champions announcing both fights Tuesday at a news conference at Staples Center in Los Angeles, which will be the site of the card on Sept. 28 (Fox PPV, 9 p.m. ET).

Those fights will, along with Spence-Porter and the previously announced co-feature between super middleweight world titlist Anthony Dirrell and former titlist and mandatory challenger David Benavidez round out the four-fight pay-per-view broadcast.

“Barrios and Akhmedov is a tantalizing matchup of two rising, unbeaten fighters going toe-to-toe for their first title, while Lopez and Molina are both known for engaging in dramatic wars,” said Tom Brown of TGB Promotions.

Barrios (24-0, 16 KOs), 24, of San Antonio, has steadily raised his competition level in recent impressive performances, including a second-round knockout of Juan Jose Velasco on May 11.

“This is the fight that will solidify me as one of the top [junior welterweights] in the world,” Barrios said. “Batyr Akhmedov was one of the top amateurs in the world and has fought some really good fighters in the pros. I must beat him to accomplish my goal of winning a world title. I live for these moments, and the world will see my talent. I’m going to bring victory home to all of Mexico and my Mexican American fans in the States.”

Akhmedov (7-0, 6 KOs), 28, who was born in Uzbekistan, lives in Russia and represented Turkey in the 2016 Rio Olympics, had such a deep amateur career that he has moved quickly as a pro. He has already defeated experienced fighters such as Viktor Plotnikov and Ismael Barroso.

“I am the eighth child in my family and we had a very difficult and poor upbringing, so I know what it means to persevere during hard times,” said Akhmedov, who will be fighting in the United States for the second time. “I only started boxing when I was 18 years old. I spent about four hours a day on the road to get to and from the gym. I really love this sport. I know what it means when people tell me that I won’t be able to achieve something. At 20 years old, I became a national champion. At 22, I was on the Olympic team.

“I was successful in many of the tournaments that I took part in. I always tried to find a way to victory. I know that it will not be easy for me on Sept. 28, but I will find a way to become a world champion.”

Lopez (36-8, 19 KOs), 35, of Riverside, California, is coming off a hard-fought majority decision loss challenging then-welterweight world titlist Keith Thurman in January in a fight in which Lopez nearly stopped Thurman in the seventh round.

“It’s going to be an all-action fight,” Lopez said. “Molina is always in good action fights. He brings power to the table. California and the world will see that on Sept. 28. I’m excited to be back in the ring on a big card.”

Molina (30-8, 24 KOs), 38, of Covina, California, a former lightweight and junior welterweight world title challenger, will also be looking to rebound from a defeat, a disputed 10-round decision loss to Omar Figueroa Jr. on Feb. 16.

Molina was supposed to return on July 20 to face former junior welterweight titlist Sergey Lipinets on the Manny Pacquiao-Thurman pay-per-view undercard in Las Vegas. But Molina withdrew the day before the bout after throwing his back out.

“This is just another day in the office for me,” Molina said. “This is an all-action, California brawl, and the fans are definitely going to get their money’s worth from this one. I’m really excited to be fighting on this big pay-per-view card with so many great, electrifying boxers.”

PBC also announced that welterweight Robert Guerrero, a former two-division world titleholder, and junior middleweight prospect Joey Spencer will be in action on the pay-per-view preliminaries (Fox Sports 1/Fox Deportes, 7:30 p.m. ET) leading into the PPV broadcast.

Guerrero (35-6-1, 20 KOs), 36, a southpaw from Gilroy, California, will face Jerry Thomas (14-1, 8 KOs), 28, of St. Mary’s, Kansas, in a 10-rounder.

“It feels great to be back in the ring, especially fighting in front of my fans at Staples Center,” said Guerrero, who retired last summer after losing his third fight in a row but returned in December and has won two low-level bouts on the comeback trail. “I had a couple tuneup fights and now I’m stepping up in competition. My boxing skills will be on display, and I’m ready to take that next step to a big fight. I’m in great shape, and I’m ready to let my hands go. Lastly, I’m dedicating this fight to the victims of the Gilroy mass shooting and I’ll be donating a portion of my purse to their fund.”

Spencer (8-0, 6 KOs), 19, of Union City, California, will face an opponent to be named in a six- or eight-round bout.

“It was really exciting to find out that I would be on a card of this magnitude,” Spencer said. “I just want to keep becoming a better pro each time I get in the ring. This experience is a big part of it.”