NEW YORK — Jermall Charlo got more than he bargained for. Much more.

The middleweight contender was scheduled to fight Willie Monroe Jr. until the fighter tested positive for a banned steroidal substance one week ago. Matt Korobov was slated to fight in an eight-round stay-busy fight on the undercard. He was sleeping when he received the call from his manager, Mike Borao, asking if he wanted to step into the PBC on FOX main event.

The Russia native didn’t hesitate. He’d been waiting so long for an opportunity like this one. And he delivered, even if he came up just short on the judges’ scorecards. At least two of them.

Korobov’s laser overhand left couldn’t miss its target Saturday in Brooklyn at Barclays Center. It racked up points all night. He seemed to be headed to a potential victory until the final round. Charlo cracked Korobov with a left hook that sent him reeling, and then followed up with a bundle of power shots. Somehow, Korobov stood up to the punishment, even though more than 90 seconds remained.

He was beaten from pillar to post in Round 12, though he staged a late rally. Ultimately, the round didn’t factor into the cards. Steve Weisfeld and Max Deluca scored it for Charlo, 116-112. Larry Hazzard Jr. delivered an outlandish tally of 119-108 for Charlo.

“I used everything that happened tonight as motivation in the 12th round,” said Jermall, referring to his twin brother Jermell’s controversial decision defeat to Tony Harrison in the co-feature. “I haven’t been that far in a fight in a couple of years. It felt good to be in there, get hit and bang with someone. He was an experienced guy who will make me better.

“I had fun in there with an opponent like that. I got the win and that’s the main thing. I still feel I’m the best in the world. I just need to prove it to the rest of the world.”

Charlo (28-0, 21 knockouts) held a title at 154 pounds before he climbed up to middleweight. The 28-year-old made quick work of his only two 160-pound opponents; Korobov was different.

The 35-year-old claimed gold at the World Amateur Championships twice. His lone pro defeat came in a title challenge of Andy Lee in 2014, a sixth-round KO in a fight he was winning.

Korobov (28-2, 14 KOs) capitalized on the unexpected opportunity with accurate punching and pressure. He held his own in exchanges with one of the biggest punchers in the sport, though his right eye began to swell shut around the midway point. Every time Jermall attacked, Korobov countered with an overhand left. Mostly, they found their mark and scored with the judges.

“I thought that I won the fight,” said Korobov. “It was definitely a fight that could have gone either way, but I believe the people know that I won. I’m the most avoided fighter in boxing and I showed why tonight. I hope this performance will get me another title fight.”

It should. Canelo Alvarez reigns over the 160-pound division, but there’s plenty of other key players in one of boxing’s best weight classes. And now, you can insert Korobov to the mix.

Despite the unexpected struggle, Charlo held on for the victory. He continues to seek his first major fight, whether it comes against Alvarez, Gennady Golovkin or Daniel Jacobs.