Six months after his shocking upset of unbeaten Anthony Joshua in New York's Madison Square Garden, Andy Ruiz Jr. will enter Diriyah Arena in Saudi Arabia on Saturday as the defending unified heavyweight champion (DAZN, noon ET). 

It's a notion that didn't appear likely when Ruiz (33-1, 22 KOs), a 30-year-old native of Imperial, California, accepted the fight as a late replacement and massive underdog. Yet one left hook to the ear of Joshua in Round 3 and a TKO win four rounds later, Ruiz had turned the division upside down by becoming the first heavyweight champion of Mexican descent.

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With his unassuming physique and happy-go-lucky persona, Ruiz has played the role of modern-day James "Buster" Douglas like he was picked from central casting. Now, in possession of three of four recognized titles, "The Destroyer" can become the singular power broker in this renaissance heavyweight era if he can upset Joshua a second time. 

"I don't want these beautiful belts to go away," Ruiz said at this week's final press conference. "Remember, I've been doing this since I was six, it's finally paying off, and no way I'm going let these belts go. I'm going to die trying and do anything that's possible to get that victory. It's been a long journey, a long roller coaster in my life, and no way I'm going to let these go."

Getting there will be interesting for Ruiz. In some ways, with his quick hands and combination punching, he may be the kind of Kryptonite that will always give the 6-foot-6 Joshua (22-1, 21 KOs) problems by exposing his robotic style. Yet Joshua also remains the betting favorite in the rematch for many of the same reasons he was the first time around -- most notably that Ruiz has lingered for years as a solid, yet unspectacular contender. 

Joshua will hold advantages of four inches in height and eight inches in reach. He's also the more proven finisher having knocked out the likes of Wladimir Klitschko and Alexander Povetkin. That won't matter, however, if he enters the ring with a shaky psyche or damaged fighting spirit.

"Your mind is the biggest muscle in the body," Joshua said. "I just use that to my advantage. Positive self-talk is important. You have to really believe it in your heart, not just your mind."

While Ruiz showed plenty of heart to get up from an knockdown and do the same to Joshua, the answer as to whether the left hook that shook up Joshua's equilibrium (and never the same) can only be answered in the rematch. 

The co-main event will see a familiar face to the heavyweight ranks as Povetkin takes on Michael Hunter. The 40-year-old Russian rebounded from his knockout loss to Joshua by scoring a decision win over Hughie Fury in August. Hunter (18-1) has won six straight with his lone loss coming to Alexander Usyk in 2017.

Saturday's festivities are littered with some big names in the heavyweight ranks, including a couple of important fights on the undercard. Dillian Whyte looks to continue his climb back into title contention when he battles with Mariusz Wach, and Filip Hrgovic takes on Eric Molina for the WBC international heavyweight crown. 

Fight card, odds

FavoriteUnderdogWeightclass

Anthony Joshua -200

Andy Ruiz Jr. (c) +170

Unified heavyweight titles

Michael Hunter -200

Alexander Povetkin +160

Heavyweights

Dillian Whyte -2500

Mariusz Wach +900

Heavyweights

Filip Hrgovic -2500Eric Molina +900Heavyweights

Prediction 

Just as easy as it is to ponder whether Joshua is damaged goods or a broken fighter after losing his unbeaten invincibility is the fact that Ruiz has never quite looked to be as dangerous and committed as he looked in pulling the upset. 

In some ways, Ruiz benefited from a perfect storm. Rumors of a rattled Joshua having been knocked out in sparring shortly before the fight could've certainly left him vulnerable. Ruiz then landed the perfect singular punch that left Joshua unable to fully regain his faculties. 

On more even terms in the rematch, emanating from a neutral site that probably only favors Joshua due to the lack of distraction and less pressure, it's hard to knock the oddsmakers in going back to the well on tabbing Joshua as the favorite. 

Has the British megastar shown flashes of a vulnerable chin in the past? Without question. The difference is how often he fought well through adversity and been able to right the ship on the kind of stages -- including in front of 90,000 fans when he got off the deck against Klitschko -- that Ruiz had never been exposed to before their first fight. 

It may seem like an easy bet to pick the man coming off the knockout win who is also the better technical boxer to put forth a repeat performance. But Ruiz is far less of a proven commodity when it comes to being taken serious as an elite fighter. He also doesn't have a particularly long history thriving in the latter rounds against top opponents, which he'll potentially have to do should Joshua fight a much more technical bout behind his jab. 

The fact that Joshua finally gave in to years of critics wondering whether he carried too much bulk to be an effective boxer by appearing to have shed muscle ahead of the rematch shows you his commitment level in getting back to the basics. Speed was the difference in their first fight and one can expect Joshua to rely on his length to keep Ruiz on the outside, where he is largely ineffective. 

Should Joshua prove successful in dictating the terms, Ruiz will eventually have to take chances to get inside. That's where Joshua's proven track record of finishing opponents once he has them hurt likely produces the same result most haphazardly predicted ahead of their first meeting. 

Ruiz is a fine boxer with heart and deceiving speed. He's also small in this super heavyweight era and has a track record for lacking motivation. Unless Joshua is broken internally from the aftermath of having been clipped, this is a matchup that his size, strength and athleticism alone should be enough to help him win. 

Upset him once? That's heavyweight boxing. But to do it a second time, Ruiz will need to prove that he has evolved into a truly elite fighter. The jury remains out on the prospect of lighting striking more than once. 

Pick: Joshua via TKO9