Just 21 days after defeating Alberto Guevara by unanimous decision, Hugo Ruiz will be facing WBA junior lightweight tileholder Gervonta Davis on Saturday at the Dignity Health Sports Park in Carson, California.

And in a twist, this time around, Ruiz is the late replacement.

Back on Jan. 19, Ruiz (39-4, 33 KOs) was scheduled to face Jhack Tepora for the WBA interim featherweight title, but after the Filipino fighter missed weight by more than five pounds, it was Guevara who stepped in to face Ruiz as the opening bout on the Manny Pacquiao-Adrien Broner pay-per-view undercard at the MGM Grand in Las Vegas.

Just a few days after that assignment, Ruiz would dutifully go back to the gym and prepare for his next outing. And after Abner Mares, who was originally slated to face Davis this Saturday night, pulled out of this fight with an eye injury, it was Ruiz who got the call to come out of the bullpen.

It turned out he was already getting warmed up, having gone back to the gym the following Tuesday after his most recent victory. Now he gets to face one of the best fighters in the division.

"I've seen [Davis] fight, of course, a few times and I know he's a counter puncher," Ruiz said during a conference call with reporters. "He looks for the knockout just like me. So this could be very electric starting early because, as you well know, I'm also a guy that looks for the knockout from the first round. So that's what I've seen and it should be exciting."

Ruiz admitted that the rather pedestrian nature of the Guevara fight allowed this quick turnaround.

"If the fight would've been more physically draining, if it would've been a toe-to-toe battle where I would've received a lot of punches and stuff, then maybe I would've not taken this fight," said the 32-year-old from Mexico. "But I continued my training leading up to the fight with Guevara and I just continued it because, again, I felt physically well after the fight. There were no major damages."

Davis isn't just a powerful puncher, he's one who does it out of the southpaw stance. Many boxers are reluctant to face left-handers on late notice, but Brown pointed out that Ruiz had been training six weeks to fight a southpaw on that card on Jan. 19.

"[Ruiz] is a very, very tough kid. He was in shape," said Tom Brown, who is one of the promoters of the PBC event. "He went right back to the gym after his fight on Manny's card."

Hugo Ruiz, left, defeated Alberto Guevara by unanimous decision on Jan. 19. Christian Petersen/Getty Images

Ruiz began his career in 2006 as a junior bantamweight and gradually worked his way up to featherweight. He is actually listed as being four inches taller than Davis (5-foot-9 to 5-foot-5), but taller doesn't necessarily mean bigger and stronger. What's alarming for Ruiz is he has been stopped in three of his four losses, all of them at the junior featherweight limit or below. Now, Ruiz is facing perhaps the most physically imposing 130 pounder on the planet.

"I feel very comfortable at this weight," Ruiz said. "If I was 126, if I was planning for 126 this Saturday coming up, I wouldn't have made it because I'm already going to make 130. That's how strong I feel at this weight, so that does not pose a problem for me against Gervonta Davis."

Davis (20-0, 19 KOs), who was actually in attendance for the Pacquiao-Broner card, but didn't get a chance to see Ruiz fight, said he believes Ruiz is more aggressive than Mares.

"I think [Ruiz] has more pop on his punches," Davis said. "I just watched a little clip of him, I haven't studied him like that. I just watched a little clip once I knew who I was fighting just to be aware of what I have in front of me."

Like Mares, whose best days were at 118 and 122, Ruiz is a boxer moving up in weight. Davis had received some criticism for facing smaller guys.

"Vasiliy Lomachenko, he fought someone that was two weight classes under him and not only one time, he fought another person that was smaller than him: [Guillermo] Rigondeaux and Miguel Marriaga," Davis said.

Davis, who was more than just a bit restless over his inactivity in 2018, is just relieved to be facing anybody.

"I'm just excited to put on a great show no matter who I'm in there with. It's all about the performance that Gervonta Davis puts on and I'm here to put on a great performance," said the 24-year-old native of Baltimore.