Gennady Golovkin faces his biggest challenge yet in Daniel Jacobs

The intrigue around a Gennady Golovkin fight has usually centered on when, not if, the unbeaten middleweight champion would knock out his opponent.

Standing taller and more muscular than Golovkin at Friday’s weigh-in, Brooklyn’s Daniel Jacobs provides the most substantial obstacle yet for the Southland-based Kazakhstan champion. Golovkin needs a victory to advance to a potential mega-fight in September against Canelo Alvarez.

“This is my biggest fight. I understand that. I’m very excited,” Golovkin told reporters in his final interview session. “My last fights [knockouts of Kell Brook and Dominic Wade] were not the toughest. This is Madison Square, pay-per-view, New York … first class.

“Daniel looks good and I hope he’s the best prepared. Other boxers — everybody — has helped him. It’s more dangerous, more serious this time.”

While Jacobs has leaned on the boxing counsel of unbeaten light-heavyweight champion Andre Ward and employed innovative conditioning techniques, Golovkin,meanwhile, maintained the regimen implemented by trainer Abel Sanchez at his Big Bear gym that has led to a string of 23 consecutive knockouts.

While Golovkin has respect for Jacobs’ grit in recovering from a 2011-12 bout against a cancerous tumor on his spine, he said any kindness evaporates once he steps into the ring.

“It’s sport,” Golovkin said flatly.

Seeking his 18th consecutive middleweight title victory — two shy of Bernard Hopkins’ record — the 34-year-old Golovkin (36-0, 33 knockouts) has spent more than half of his career feeling ignored.

He couldn’t get middleweight champion Felix Sturm to fight in Germany and came to the U.S. to see champions Sergio Martinez and Miguel Cotto and popular Julio Cesar Chavez Jr. treat him as if he was a quick left-swipe reject on a dating app.

Mexico’s Alvarez handed over his World Boxing Council middleweight belt to Golovkin rather than fight him last year and has now vowed through promoter Oscar De La Hoya to meet Golovkin in September should Alvarez defeat Chavez Jr. on May 6.

“Gennady has to win on Saturday and Canelo’s got to win. If either of those doesn’t happen, a fight in September is irrelevant,” Golovkin promoter Tom Loeffler said.

“I don’t see any reason we can’t sign a deal for a fight with Canelo. If everything goes the right way, we’ll sit down the end of next week and continue to discuss it. I feel comfortable there’s no one issue that will prevent the fight.”

A reporter asked what would happen if Golovkin scored a quick knockout of the 30-year-old Jacobs (32-1, 29 KOs).

“Well, that might be a problem … ,” Loeffler said, half-grinning.

Jacobs and his manager, Al Haymon, struck a deal for the opportunity to stun the fight world and proclaim himself middleweight king during this St. Patrick’s Day weekend near his hometown.

Although the durability of his chin is considered the most important thing to watch Saturday night, the 5-1 underdog Jacobs has knocked out 12 consecutive opponents.

East Los Angeles’ former junior-middleweight world champion Sergio Mora has fought Jacobs twice, knocking Jacobs down in 2015 before going down himself five times in their September rematch.

Since Golovkin and Jacobs weighed in approximately 36 hours before the first bell — a situation that brought some outrage from veteran boxing people — Mora said Jacobs’ rehydration look was the most imposing, surprising factor to contend with.

“You’ll see how much bigger Danny will be. He’s huge the day of the fight and he can really punch,” Mora said. “He’s mentally tough and has the temperament of a guy who’s not going to relent.

“When I knocked him down, he got up, pounded his chest and told me to come on. He’s got bravado. The cancer fight has just added to his story.”

Calculatingly, Golovkin has said he’s prepared for the formidable foe.

“I understand who Jacobs is,” he said.

Said Loeffler: “This is what Gennady has always wanted. People think Danny has the biggest chance. He’s bigger, has fast hands, power. This is what motivates Gennady. This is what will allow Gennady to really show his skills. He was a little sloppy and not as focused when he was not feeling really threatened. Here, he’s going to be razor sharp.”

BOXING

Who: Gennady Golovkin (36-0, 33 KOs) vs. Daniel Jacobs (32-1, 29 KOs) for Golovkin’s WBA, IBF and WBC middleweight belts

Where: Madison Square Garden, New York

Television: HBO pay-per-view, $54.95

When: Saturday, pay-per-view portion begins at 6 p.m.; pre-PPV undercard action on Ring TV

Undercard: Roman “Chocolatito” Gonzalez (46-0, 38 KOs) vs. Srisaket Sor Rungvisai (41-4-1, 38 KOs) for Gonzalez’s WBC super-flyweight belt; Carlos Cuadras (35-1-1, 27 KOs) vs. David Carmona (20-3-5, 8 KOs), super-flyweights; Ryan Martin (17-0, 10 KOs) vs.Bryant Cruz (17-1, 8 KOs), lightweights

lance.pugmire@latimes.com

@latimespugmire