LOS ANGELES -- Junior middleweight titleholder Jermall Charlo and mandatory challenger Julian "J Rock" Williams let each other know often that they did not like each other leading up to their fight. And then Charlo let him know who was boss once they got into the ring.

Charlo dominated Williams before brutally knocking him out in the fifth round Saturday night in the co-feature of the Jesus Cuellar-Abner Mares featherweight world title fight at the Galen Center on the USC campus.

Charlo (25-0, 19 KOs) scored three knockdowns as he retained his 154-pound belt for the third time in a fight many believed would be the toughest of his career. Instead, it turned out to be one of the easiest and nowhere near the 50-50 fight many predicted.

Jermall Charlo, left, retained his junior middleweight title with an impressive victory over Julian Williams. Stephanie Trapp/Showtime

"I did what I was supposed to do," Charlo said. "I'm very happy with my performance -- I listened to my trainer [Ronnie Shields]. I trained hard for this fight. I stayed in the gym the whole time. No matter what, people have to respect my accomplishments. He just wasn't on my level. I told everyone what I was going to do since the fight was announced."

After virtually nothing happened in the opening round, the action picked up considerably in the second round. Charlo landed a stiff jab down the middle that dropped Williams to his backside.

Williams (22-1-1, 14 KOs) was on shaky legs when the fight resumed but eventually regained himself later in the round when he nailed Williams with a clean right hand.

Charlo continued to get through with a long jab and Williams, in his first world title bout, had a hard time getting past it.

Punch stats Punches Charlo Williams Landed 46 48 Thrown 175 181 Percent 26% 27% -- Courtesy of CompuBox

In the fifth round, Charlo turned out the lights. He landed a massive right uppercut that spun Williams halfway around and dropped him. He was badly hurt and barely made it to his feet.

"I was fine; I knew I could get up and keep going," Williams said.

He appeared to be in rough shape, but referee Wayne Hedgepeth let the fight continue and Charlo wasted no time.

"I knew I was going to win. He was badly hurt after the knockdown," Charlo said.

Charlo, 26, of Houston, pasted Philadelphia's Williams, 26, with punches with both hands and finally knocked him down once again with a heavy left hook, and Hedgepeth called off the fight at 2 minutes, 6 seconds.

"I just got caught. He just caught me with a shot," Williams said. "All I wanted to do is win."

When the fight was over Charlo, the twin brother of fellow junior middleweight titlist Jermell Charlo, still was in no mood to make nice with Williams, brushing off his post-fight overtures to embrace as the crowd booed his unsportsmanlike conduct.

Charlo later apologized.

"I just want to tell Julian Williams I'm sorry," Charlo said. "Leading up to this fight Julian Williams talked, and I held it in. I did what I had to do to become the champion of the world and I deserve my respect. He disrespected me all the way up to the fight.

"I said I don't want your congratulations, I want your apology. I don't care what they say, I knocked him out. I've never disrespected this dude, never, until I knocked him out."

Charlo said he wants to unify the division, although he and his brother have said they would never fight each other.

"I want to unify, the WBO with Canelo [Alvarez], the WBC or WBA. Where are you [Canelo]? I want to prove I'm the best junior middleweight in the world," Charlo said. "None of them are on my level. I've worked very hard throughout my career. I haven't been given anything."

Lipinets KOs Zappavigna in eliminator

Junior welterweight Sergey Lipinets, left, defeated Lenny Zappavigna with a ninth-round knockout to earn a shot at a world title. Stephanie Trapp/Showtime

Russian junior welterweight Sergey Lipinets (11-0, 9 KOs) scored a ninth-round knockout of Australia's Lenny Zappavigna (35-3, 25 KOs) in a bloody, action-packed bout to earn a world title fight.

With the victory in the official eliminator, Lipinets earned a mandatory title shot against world titleholder Julius Indongo (21-0, 11 KOs), of Namibia, who won a 140-pound belt last week when he shockingly knocked out Eduard Troyanovsky in 42 seconds.

"I'm very happy with my performance. We've worked on adjusting during fights and that worked very well for me," Lipinets said through a translator. "I was hoping for the knockout, but my trainer said to keep working and the stoppage will come. This was my toughest fight. It's bloody and rugged but no problem for me."

They waded into battle from the opening bell and never let up, blasting each other throughout the fight.

Zappavigna, 29, had a big fourth round, hurting Lipinets, 27, with hard shots and busting open a very bloody cut over his right eye during a fierce exchange. But Lipinets came back big in the fifth round when he floored Zappavigna and opened a cut over his right eye with a clean left hook and continued to rock him in the round.

The sixth round was another violent one as they fought toe to toe. Before the seventh round, referee Tom Taylor had the ringside doctor examine Zappavigna's cut. In the eighth round, as they continued to hammer each other, Lipinets creamed Zappavigna with a clean right hand to the head and he went down to his backside, and Taylor counted him out at 1 minute, 23 seconds.

"I left it all in the ring," Zappavigna said. "I fought my heart out and I came here to give it my best. Even though I'm disappointed with the loss, I am at peace with the result because I know I couldn't have done anything else. I wish Sergey all the best in his world title fight. I know my fans are behind me and I'm bringing pride back to Australia."