Sergey Kovalev figures he's known Igor Mikhalkin since he was about 17, back when they were amateur teammates in Russia.

Come Saturday, that will mean nothing.

"We were like friends, but only friends can beat on each other and don't be upset at each other," Kovalev said.

They meet in the Theater at Madison Square Garden for the WBO light heavyweight title that Kovalev (31-2-1, 27 KOs) regained in his last fight after dropping it in the first of his consecutive losses to Andre Ward.

Kovalev has changed plenty since then, but "Krusher" wants to show his punishing power hasn't gone anywhere.

"Saturday night will be an interesting fight because we will beat each other very, very hard," Kovalev said.

The match against Mikhalkin (21-1, 9 KOs) is one of two title fights in the 175-pound division on Saturday's card, which will be televised by HBO. Dmitry Bivol (12-0, 10 KOs), another Russian, defends his WBA belt against Cuban Sullivan Barrera (21-1, 14 KOs) in the other.

Barrera was initially offered the fight against Kovalev in what would have been a matchup between fighters whose only losses were to Ward. Instead, he took less money for the shot at Bivol's belt and Kovalev ended up with Mikhalkin.

They went separate ways since their amateur days, with Kovalev, 34, moving on to win three light heavyweight titles and fight in major bouts in the U.S. Mikhalkin, now based in Germany, stayed behind to do his fighting in Europe, and now he has a chance to make a worldwide name for himself if he can knock off Kovalev.

"This is most likely the most important fight in my career," Mikhalkin said. "This is the greatest opponent I've ever fought."

But it was a damaged one after the losses to Ward, the first by a narrow decision but the second when Kovalev was stopped in the eighth round. He easily won back the WBO belt that Ward vacated after retiring when he stopped Slava Shabranskyy at MSG in November. But he realized he still needed to re-evaluate his training and travel.

"To lose after being world champion, such a dominant world champion, is a bitter blow. Some guys never recover from that," promoter Kathy Duva said. "But a rare few take an honest look at the way they are doing things, they change what needs to be changed and no matter how difficult, no matter what you have to give up to do it. This is hard. Sergey is not afraid of hard, as we all know."

Now trained by Abror Tursunpulatov, Kovalev believes rededicating himself could bring him to a level he hadn't reached even when he was rolling through everyone in front of him.

"I am motivated for the new chapter in my boxing career, and I showed in the last fight that I am back and now I am on my way to my goals," Kovalev said.