Andy Ruiz Jr. overcame a knockdown and additional trouble Saturday night to avoid ending up on the wrong end of a huge upset.

Ruiz got up from a second-round knockdown, recovered from Chris Arreola’s left hook early in the third round and beat the veteran heavyweight by unanimous decision in their 12-rounder at Dignity Health Sports Park in Carson, California. Judges Lou Moret (118-109), Pat Russell (118-109) and Zachary Young (117-110) scored their bout by wide distances for Ruiz, who was listed by most Internet sports books as a 25-1 favorite entering their FOX Sports Pay-Per-View main event.

A resilient Ruiz regained control of their fight after his struggles in the second and third rounds and mostly out-boxed Arreola over the final nine rounds.

Ruiz, of Imperial, California, improved to 34-2 (22 KOs) by winning his first fight since losing the IBF, IBO, WBA and WBO titles back to Anthony Joshua in their rematch 16 months ago. Arreola (38-7-1, 33 KOs, 2 NC), of Riverside, California, lost a second straight fight.

“You know, Chris Arreola, he’s a veteran,” Ruiz told FOX Sports’ Heidi Androl after his victory. “He’s a hard puncher and, you know, we did what we had to do. We won the victory. But remember, I was the lowest of the lowest and I had to come back to the ladder. Yup, keep booing, bro. It’s all good. But like I said, we did what we gotta do. And thanks to God that we got this victory and now to the next.”

Arreola acknowledged that Ruiz won their bout, but he cursed out the judges because none of them gave him more than two rounds. Young scored two rounds for Arreola (the second and third), whereas Moret and Russell scored one round apiece for the longtime contender (the second).

“I respect the judges, but today, I always said beauty is in the eye of the beholder,” Arreola said. “They like a butterface. Everything’s pretty but their face. Honestly, man, did he win? Fine. But don’t tell me you’re only gonna give me two, three rounds. F*** that! I’m gonna be like Dr. Dre. All y’all can suck my motherf***ing d*ck!”

The 31-year-old Ruiz officially weighed 256 pounds Friday, 27½ pounds less than he weighed the day before he lost a unanimous decision to Joshua in their 12-round rematch in December 2019 in Diriyah, Saudi Arabia. Ruiz pulled off one of the biggest upsets in heavyweight history when he defeated England’s Joshua by seventh-round technical knockout in June 2019 at Madison Square Garden in New York.

Trainer Eddy Reynoso, renowned for his work with four-division champion Canelo Alvarez, worked Ruiz’s corner Saturday night for the first time.

The 40-year-old Arreola weighed in Friday at a career-low 228½ pounds for his first fight in 20 months. Prior to Saturday night, Arreola hadn’t boxed since he lost a 12-round unanimous decision to Adam Kownacki (20-1, 15 KOs) in August 2019 at Barclays Center in Brooklyn, Kownacki’s hometown.

Arreola got off to a strong start Saturday night, but his punch output decreased in the later rounds and he appeared to suffer an injury to his left shoulder. As they entered the championship rounds, it seemed inevitable that Arreola would lose on points.

Ruiz, clearly in control, out-boxed Arreola again in the 12th round to cruise to his convincing victory.

A right-left combination by Ruiz caught Arreola about 35 seconds into the 11th round. Ruiz’s left hook caught Arreola about 15 seconds later.

Arreola shook out his injured left arm after absorbing that left hook. Ruiz’s right hand got Arreola’s attention with about 15 seconds to go in the 11th round.

A left hook by Ruiz knocked Arreola off balance 20 seconds into the 10th round. Ruiz also backed up Arreola with a jab about 20 seconds later.

Arreola didn’t throw many punches in that round, when he again shook out his left arm.

Ruiz’s right to the body caught Arreola in the ninth round. Later in the ninth, he caught Arreola with a left hook up top.

By that point in the fight, Ruiz clearly was in control.

Arreola connected with a right hand with about 1:40 to go in the eighth round. About 15 seconds later, Arreola shook his left arm and indicated that he hurt his left shoulder.

Ruiz’s left hook landed with just under 40 seconds to go in the seventh round, which amounted to three more effective minutes for the former champion.

Ruiz connected with consecutive lefts about 30 seconds into the sixth round. Another left hook by Ruiz landed just before the midway mark of the sixth round.

Arreola nailed Ruiz with a right to the side of his head about 1:20 into the fifth round. Ruiz caught Arreola with a sweeping left hook just before the fifth round ended.

Ruiz connected with a right hand with about 30 seconds to go in the fourth round. Arreola mostly defended himself during the fourth round, as Ruiz pressed the action.

After dropping Ruiz early in the second round, Arreola wobbled Ruiz with a left hook less than 20 seconds into the third round. Ruiz almost went down from that shot, too, but he came back from a squatting position and fired back with hard shots of his own that made Arreola cautious.

The action slowed down most of the rest of the remainder of the third round, as Arreola and Ruiz seemed more mindful of defense. Ruiz did drill Arreola with a right hand toward the end of the third round, but Arreola blasted Ruiz with a right hand of his own before that third round ended.

Arreola landed a short right hand that dropped Ruiz to one knee early in the second round. Ruiz got right to his feet after suffering that knockdown and seemed more disappointed than hurt.

Arreola also landed two hard left hands that got Ruiz’s attention with just under 20 seconds to go in the second round.

An overhand right by Ruiz made Arreola hold him just after the halfway point of the first round. Another right hand by Ruiz caught Arreola with about 40 seconds to go in the opening round.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.