Gennady Golovkin celebrates after knocking down Vanes Martirosyan in their middleweight title fight on Saturday night. Photo: Chris Carlson/AP
Gennady Golovkin celebrates after knocking down Vanes Martirosyan in their middleweight title fight on Saturday night. Photo: Chris Carlson/AP
Gennady Golovkin, left, used the jab initially against Vanes Martirosyan. Photo: Chris Carlson/AP
Gennady Golovkin, left, used the jab initially against Vanes Martirosyan. Photo: Chris Carlson/AP
Gennady Golovkin stands in a corner after knocking down Vanes Martirosyan. Photo: Chris Carlson/AP
Gennady Golovkin stands in a corner after knocking down Vanes Martirosyan. Photo: Chris Carlson/AP
Gennady Golovkin shakes hands with Vanes Martirosyan after the bout. Photo: Chris Carlson/AP
Gennady Golovkin shakes hands with Vanes Martirosyan after the bout. Photo: Chris Carlson/AP
Gennady Golovkin retained all his middleweight titles to equal Bernard Hopkins' record of 20 consecutive successful defences. Photo: Chris Carlson/AP
Gennady Golovkin retained all his middleweight titles to equal Bernard Hopkins' record of 20 consecutive successful defences. Photo: Chris Carlson/AP

LOS ANGELES – Gennady Golovkin equalled the record of 20 straight world middleweight title defences with a devastating second-round knockout of Vanes Martirosyan on Saturday night to retain his WBA and WBC belts.

Golovkin ended the fight with a vicious series of right and left combinations that floored the heavy underdog Martirosyan, who appeared doomed from the outset of the hastily arranged fight at the StubHub Center.

“The first round I was just looking, because I know he is a good fighter,” the 36-year-old Golovkin said. “The second round, it was true business.”

Martirosyan was in big trouble from the beginning of the second round as Golovkin rendered the challenger helpless by landing a right uppercut on the chin. 

He followed with a few stinging jabs, and then a full throttle left hook and straight right on the ropes that put Martirosyan down for good at 1:53 of the round.

The American tried to get up before the 10 count, but slumped forward, ending up face down on the canvas.

Golovkin, who is boxing’s longest-reigning current world title-holder, is now unbeaten in 39 fights, including 34 by knockout.

Martirosyan was a last-minute replacement following the cancellation of the Kazakh’s much anticipated rematch with Canelo Alvarez of Mexico.

The rematch was cancelled because of Alvarez’s two failed drug tests in February, followed by his suspension by the Nevada State Athletic Commission on April 18.

Alvarez will be free to fight once his suspension ends in August.

Saturday’s event was moved from Las Vegas to south central Los Angeles, and Golovkin fought for a fraction of the money he would have received for a fight against Alvarez.

With the victory, he now joins Bernard Hopkins for the division record of 20 successful title defences.

Golovkin (38-0-1, 34 KOs) is now in line to surpass Hopkins in the fall when he hopes to finally get that rematch with Alvarez.

“I want everybody,” said Golovkin. “It doesn’t matter to me. I am still the champion... guys, come and take my belts.”

The 31-year-old Martirosyan, who normally fights at light middleweight, was completely outclassed as he stepped up a division to face the hard-hitting Golovkin.

“It was like being hit by a train,” Martirosyan said. “That is the hardest puncher I have ever faced. He surprised me with his power. He is a hell of a fighter.”