LOS ANGELES — Gennady Golovkin is used to this.

Not to a switch in opponent mid-camp. That, of course, he wasn’t prepared for after Canelo Alvarez tested positive for the banned substance clenbuterol, cancelling their mega fight set for May 5.

But he’s accustomed to training for middleweight title bouts against opponents who are given little to no chance of posing any threat. When you make 19 consecutive 160-pound title defenses, you’re bound to face all sorts of foes. And for the majority of GGG’s career, he’s competed against middling boxers while the upper echelon of the sport was none too eager to step in the ring with him.

In Vanes Martirosyan, Golovkin will face a solid boxer, one with an Olympic pedigree. The 32-year-old Armenian’s three losses all came via decision to elite fighters. And there’s no doubt Martirosyan is better than many of the boxers who have challenged Golovkin for his titles.

But Martirosyan is coming off a two-year layoff, and he’s a contender at 154 pounds, not 160, the weight at which Saturday’s HBO fight at StubHub Center in Carson, California, will be contested. He’s understandably a massive underdog.

It’s commonplace for athletes to take overmatched opponents lightly. It’s only natural. James Toney made a habit of this during his storied career. But Golovkin has always been the very model of consistency.

“For many years and in many cases, my opponents have been underestimated,” Golovkin said Wednesday during a sit-down with reporters, opting to speak in Russian with a translator to his right, rather than English, which he usually conducts interviews in. “I want to remind you, eight years I’ve kept the middleweight title.

“For eight years, I was standing as a champion and I was not refusing to fight anybody. So this is a big fight, it’s a championship fight.”

Surely, Golovkin has never avoided anyone, it was he that was being avoided by the likes of Miguel Cotto and Sergio Martinez. So he fought who was available and continued to pile up successful title defenses.

For a long time, those bouts took place in Europe, until he finally broke through with his HBO debut in September 2012 with a stoppage of Grzegorz Proksa. One by one, they all failed to see the final bell, former titleholders and contenders alike. Daniel Geale. Matthew Macklin. Gabriel Rosado. Curtis Stevens. Martin Murray.

And then, there were mostly unknown foes like Willie Monroe and Dominic Wade.

None of them presented even a remote challenge to GGG, and Martirosyan doesn’t figure to either.

It was only when Golovkin (37-0-1, 33 knockouts) stepped up to the elite level last year that it was truly evident just how special of a fighter he is.

He fought 24 rounds with Daniel Jacobs and Alvarez, winning the first bout and fighting to a draw in the latter, and although both bouts were close, public sentiment is that Golovkin deserved the decision in each fight.

He was set up for another encounter with Alvarez, an event that stood as the biggest boxing has to offer in 2018, and the $20 million-plus payday that accompanies it. Instead, Golovkin will settle for a purse that figures to be just a fraction of that, before a far smaller audience, and with much less fanfare surrounding it.

This is, of course, no fault of Golovkin’s. He didn’t fail any drug test. But all the same, Golovkin must deal with the disappointment and make sure he takes care of Martirosyan in proper fashion. The rematch with Alvarez will be waiting for him in September, provided he wins, as expected, and emerges from Saturday’s bout without injury.

“Life is a very interesting thing and if you focus on the negative, you’re not going to last for a very long time,” Golovkin, 36, said. “I like my work. I like my sport. That’s what keeps my concentrated.”

“I’m completely focused on my May 5 fight, when we’re done with this fight then we’ll talk about the next fight.”

Golovkin endured another 10-week camp with his longtime trainer, Abel Sanchez, at his Big Bear Summit camp in Southern California, and the coach remains amazed at his fighter’s work ethic.

Whether he’s fighting on the biggest stage or in just another obut, Sanchez says Golovkin never loses sight of his goal. And with a victory on Saturday, he’ll match the legendary Bernard Hopkins’ record of 20 consecutive middleweight tight defenses, a testament to GGG’s longevity, consistency and commitment to his craft.

“It’s completely rare. In over 40 years I don’t think I’ve even seen a fighter that is just so focused on what he’s doing, on what’s next, that loves his work,” said Sanchez, who also trained Hall of Famer Terry Norris.

“I think because of his background, because of his Kazakh upbringing and the Kazakh system that they have over there, they’re very focused. We’re trying to equal the record right now of Bernard Hopkins, and if you look at Bernard’s record, he fought Robert Allen three times, Antwun Echols twice.

“We haven’t had any rematches. I think that people put him on such a pedestal they expect him to fight the top guys every time out. He fought three elite guys in a row, and if he’s going to continue fighting elite guys three or four times each year, we’ll be fighting [Anthony] Joshua next year. There aren’t that many elite guys.”

Sanchez is perhaps selling the stacked 160-pound division a little short. There’s plentiful tantalizing matchups that await Golovkin after Martirosyan is out of the way. Jermall Charlo looms as a legitimate threat, a blend of size, speed, athleticism combined with a ruthless edge. There’s also the rematch with Jacobs, who Sanchez swears hasn’t been the same fighter since he faced GGG.

And, of course, the rematch with Canelo that’s bound to happen in September. But before Golovkin is willing to even discuss any of those matchups, he wants to — and needs to — take care of business on Saturday.

Mike Coppinger is the Senior Writer for RingTV.com. Follow him on Twitter: @MikeCoppinger