Hrgovic (21-1, 16 KOs) survived a second-round knockdown, a cut across his right eyebrow and eight mostly one-sided rounds getting sliced and diced against the more explosive Itauma (14-1, 12 KOs), only to show off a granite chin en route to outlasting and stopping his suddenly fast-faded opponent in the ninth round at O2 Arena.

"I said from the beginning that Itauma is just too immature and too inexperienced to put him in a fight like this against Hrgovic," Sanchez told The Ring. "Itauma threw a lot of punches and expended a lot of energy. I thought that if we can take this kid into the second part of the fight, we're going to be able to do what we want. We may lose a lot of rounds in the beginning, but that's not where the fight would be for us. I thought that the fight would be won from the sixth round and onward.

"The worrisome part for me was that Itauma was a little faster than I anticipated. He was quick with his hands, and we just couldn't catch up with that speed. We were getting caught with some really good straight left hands."

Sanchez said that he could see Itauma showing signs of fatigue in the first round. After they weathered a storm following a flash knockdown in the second round, Sanchez said he "saw a little chink in Itauma's armor" as Hrgovic started catching him with straight right hands.

"We wanted Itauma to come straight at us and expend energy — and sure enough, he did," Sanchez said. "We planned to have presence and be in front of this man, and not necessarily throwing punches and combinations, but touching him with the jab. Now, with the punches that he did hit Hrgovic with, he may have knocked out a lot of the other top 10 heavyweights, but Hrgovic is a guy who's never been really hurt.

"We were confident with our training and conditioning going into the fight. Hrgovic came for camp in Big Bear, California, and was willing to do everything that I asked. After studying a little bit of Itauma, I saw the fast hands and explosiveness, but I didn't think he knew how to punch yet, or that he was a big puncher."

After eating a tremendous uppercut in the fifth, Hrgovic had his own share of success in the seventh and eighth as Itauma began to show immediate signs of fatigue.

"By the eighth, I told Filip to apply more pressure and extra work because I could see that Itauma was gassing out," Sanchez said. "It was a culmination of shots and exhaustion that forced the fight to be stopped in the ninth.

"It was strange to see how Itauma's body was contorting; the movement of legs and upper body was very strange. It looked like he was seriously hurt. I'd never seen that before, how the body completely quit like that all of a sudden. Itauma's fatigue made it seem like he was drunk, because his body couldn't function and he was doing things that I'd never seen before."

With Itauma unsteady on his legs, wobbling all over the place and falling back onto the ropes, trainer Ben Davison threw in the towel almost simultaneously as referee Howard Foster stepped in to stop the fight with Itauma collapsed in the corner. The 21-year-old was later stretchered out of the ring.

Itauma was up 80-71, 80-71, 79-72 on the scorecards at the time of the stoppage, which came with 33 seconds left in the ninth.

"Filip's conditioning proved to be the difference for him winning the fight," Sanchez said. "The guys that I've trained, whether it be Gennadiy Golovkin, Terry Norris, or anyone else, have always been strong, if not stronger, in the second half of the fight than they were in the first. They are always in great shape. I think that the last three rounds are the most important rounds of a fight. And if you train that way, you're going to have success.

"Itauma didn't have the experience to be able to deal with a guy who wasn't going to go away. Until you've been there, you really don't know what it's like to extend yourself for a 12-round fight against a guy that's been there already."

According to CompuBox, Itauma landed 163 of his 416 shots while Hrgovic connected with 90 of his 346 punches.

After the fight, a clip of Itauma previously stating that he doesn't spar for 12 rounds went viral.

The 21-year-old Itauma came into the clash with just 31 rounds of pro experience under his belt. On the flipside, Hrgovic, a 2016 Olympic bronze-medalist, came in with 105 rounds and wins against the likes of Zhilei Zhang, Joe Joyce, David Adeleye and David Allen.

"To say that he doesn't train for 12 rounds, and to not do that in the gym, for Moses, or for his team, I think that's suicide," Sanchez said. "If you're not prepared physically and mentally for 12 hard rounds of work, then you're not going to be successful.

"It was evident in this fight that this kid didn't work on differentiating himself from his last amateur fight to his 15th professional fight. So there has to be a difference. He still punches like an amateur. There have to be changes made along the way to prepare you for the elite level. The elite level is a group that is very hardened and very tough and ready for 12-round fights.

"I think that Itauma has a lot of talent and a very, very bright future depending on how he takes this loss and how he restructures his belief in what it takes to get to the top."

The soon-to-be 71-year-old Sanchez is semi-retired these days and only focused on training Hrgovic. The Itauma fight was their fourth together.

The fighter and coach combo celebrated the dramatic win with a meal together at a McDonald's in London before heading their separate ways, Sanchez to Southern California, and Hrgovic to Croatia as the country's first-ever heavyweight champion.

Hrgovic's next test should come against IBF mandatory challenger Frank Sanchez, but it could also be a rematch against Daniel Dubois as Hrgovic attempts to avenge the lone loss of his career, if the WBO champion Dubois gets past his rematch against Fabio Wardley on October 17.

"Filip was the fighter who got me out of retirement," Sanchez said. "I've had a blessed career with a lot of moments like this one, but obviously not in the heavyweight division.

"Considering everything, you could call this the crowning moment of my coaching career. This was an extremely rewarding win for me, and I am really happy and proud of Filip Hrgovic and everything he accomplished."