As Oleksandr Gvozdyk prepares for the first defense of his WBC light heavyweight belt against Doudou Ngumbu on Saturday at the 2300 Arena in Philadelphia, Pennsylvania (ESPN, 10 p.m. ET), he is once again under the guidance of trainer Teddy Atlas.

Gvozdyk (16-0, 13 KOs) doesn't just tolerate working with the fiery Atlas. He relishes it. Gvozdyk fully understood what he was signing up for last year when he asked the hard man from Staten Island, New York, to prepare him for his first title opportunity against Adonis Stevenson last December.

"I like Teddy because he's a straight, honest person. I like honesty," Gvozdyk told ESPN.com. "Even though he's really picky, but this is the thing: It's an essential ingredient to be successful. He's always on top of every problem, every mistake. He never lets me drift -- he makes me better. And also, he's a good person.

"With Teddy, it's a challenge every day. It's crazy, but it's true. Teddy, if I'm doing good, demands better. If I do better, he demands I do even better than that. So this is Teddy. This is who he is." Oleksandr Gvozdyk

"I don't like fake [people], and Teddy is really the opposite. That's why I would rather hear that something is wrong with me and it's going to be true than looking to some compliments and it's going to be fake."

Atlas is indeed a hard man to please in the corner, Gvozdyk admits.

"It's always difficult to train with Teddy because he's always demanding to be the best, each day. No day can you drift or something. It's always difficult, super difficult, but it's worth it. We're not here to make it easy. It's no pain, no gain."

Atlas admits that he isn't for everybody. Every few weeks, a manager or promoter will inquire about Atlas' availability to train their boxers. For the most part, he declines these requests. Atlas has a conflicted relationship with boxing. He loves the purity of the sport but absolutely detests the business and unseemly side of it. Like every other individual who has decided to become a trainer, he has had relationships with boxers go sideways. To say he's cynical about the game is a vast understatement.

When Gvozdyk and his camp asked Atlas about hooking up with him prior to his title fight with Stevenson, the trainer had his usual skepticism. For Atlas, training a fighter isn't just a 9-to-5 endeavor, and he isn't the type to have a factory line of fighters he trains throughout the day.

"I just feel this responsibility that sometimes is almost overwhelming when I'm in camp to make sure that I don't fail that responsibility to someone who trusts me," said Atlas, who makes it clear that he can really train only one boxer at a time.

As he mulled the decision to work with Gvozdyk, Atlas told his camp that he was reluctant to uproot himself for a couple months away from his family in New York. But Gvozdyk assured Atlas that he would be willing to go to the East Coast to work with him. That gesture swayed Atlas to work with "The Nail."

At the end, they trained together in Oxnard, California. Yeah, Teddy is a complex character.

"With Teddy, it's a challenge every day," said Gvozdyk, who added that he views Atlas as more of a mentor than a trainer. "It's crazy, but it's true. Teddy, if I'm doing good, demands better. If I do better, he demands I do even better than that. So this is Teddy. This is who he is."

For Atlas, the decision to work with a boxer isn't just about his ability inside the ring.

"[He's] a good person, a good, decent person that I enjoy being around, that I think I can help," Atlas said of Gvozdyk. "And [he] wants to do what you're asking them to do, that is open to coaching and at the end of the day is intelligent enough to grasp things that you are teaching him."

Their union got off to a glorious start, as Gvozdyk fought a tactically disciplined fight to stop the long-reigning Stevenson in 11 rounds in Quebec City.

Now, this might surprise you, but Atlas said he wouldn't have changed a thing about Gvozdyk's performance.

"Nothing," Atlas said.

It was Atlas' opinion that Stevenson's left hand, along with Deontay Wilder's right cross, were the two most devastating weapons in all of boxing. Atlas described Stevenson as "one of the hardest punchers that I've ever seen in boxing -- ever."

For this fight, Atlas stressed to Gvozdyk that they had to take small bites, like a piranha, and get the 41-year-old Stevenson into deep water, then eventually drown him. While the game plan seemed overly cautious to some, Atlas explained that he understood that there was no margin for error.

Gvozdyk was hurt just one time in this fight, in the 10th round, as Atlas pointed out that he jabbed too close to Stevenson, leaving him vulnerable to the veteran's vaunted left hand. But Gvozdyk quickly recovered and halted Stevenson in the next round.

Teddy Atlas, who has trained the likes of Timothy Bradley Jr., said the fit with Oleksandr Gvozdyk has been ideal. "I don't want to train anyone else, to be quite frank," Atlas said. AP Photo/LA Daily News/Zuma Press/Gene Blevins

"I knew it wasn't the most popular fight plan, but it's the one that made the most sense for me, that made the most sense for my fighter," Atlas said.

In the immediate aftermath of the victory, you saw something that is rare -- a jubilant Atlas. It was evident that this victory really meant something to him. His fighter sensed that immediately.

"It was super special. This isn't just about me. It's the biggest step for my career. My dream came true, but also for Teddy, he came back, and he proved to everyone that he still is in good shape as a trainer, and also, it was really risky for him because if I didn't win this fight, all the spears would fly to Teddy," Gvozdyk said.

"I'm glad that Teddy let me work with him because it was not an easy decision for him."

The affection they have for each other is clear. But despite their admiration, Gvozdyk said he is never allowed to get too comfortable, much less complacent.

"I don't want to train anyone else, to be quite frank," Atlas said.

In the past, Atlas has been in the corners of Mike Tyson (as a young amateur), Donny Lalonde, Michael Moorer, Michael Grant, Junior Jones, Kirk Johnson, Alexander Povetkin and, most recently, Timothy Bradley Jr. Not all of these unions have worked. Some were fractured because of personality conflicts or what Atlas perceived to be character defects of the fighters. Others were purely for boxing reasons.

This relationship with Gvozdyk seems to be working.

Bob Arum, whose company, Top Rank, promotes Gvozdyk, has an idea as to why.

"You have to understand, Oleksandr is the smartest fighter, intellectually, I have ever promoted," Arum said. "And he is smart enough so he can cut through Teddy's rhetoric and get from Teddy's instructions the gems. A regular fighter might have difficulty with that because he can't get through Teddy's emotions and rhetoric."

Gvozdyk's manager, Egis Klimas, is more succinct.

"Teddy is a teacher, and Oleksandr is someone who wants to be taught," Klimas said.

This weekend, they'll head to Philadelphia to face the unheralded Ngumbu (38-8, 14 KOs), who many believe is the obligatory soft first defense for Gvozdyk. But Atlas points out that Ngumbu has beaten two undefeated fighters in his past four fights and has racked up more than 30 wins.

"This is an experienced, hungry guy, a game guy, a gritty guy," Atlas said. "He's a guy that doesn't come to just get a payday. He comes to try to win all the time."

With this assignment looming, Atlas spent the past eight weeks at the Boxing Laboratory in Oxnard preparing his pupil for their next test.

"The only part of it [the boxing business] that still rings good for me is when I'm in the gym teaching, having a guy that I think I can help, that wants to be helped," Atlas said.