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 lopsided odds were the byproduct of Martirosyan taking this fight on just 2½ weeks' notice, moving up one weight class and ending almost a two-year layoff against Golovkin.
By now, boxing fans will certainly know the situation surrounding Canelo, and the fact that he tested positive for the clenbuterol substance which saw him removed from his highly anticipated rematch against Triple G on Cinco de Mayo weekend. "It's the hardest I've ever been hit".
"Everybody want second fight, second step".
Ultimately, Loeffler and Golovkin (37-0-1, 33 KOs), 36, a Kazakhstan native fighting out of Santa Monica, California, settled on Martirosyan as the late substitute. Imagine [what he would want to fight] Golovkin, Anthony Joshua money. Golovkin retained possession of the World Boxing Council and World Boxing Association middleweight titles.
Gennady Golovkin was not expected to have too much difficulty in his pairing with Vanes Martirosyan last night but boy did he make it look easy.
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This time around, the Armenian-born challenger stood his ground in the first three minutes and landed six power punches to the champion's five.
With the victory he now joins Bernard Hopkins for the division record of 20 successful title defences.
With Canelo out, Golovkin began the search for a fighter who would agree to be in.
The fight's promoters billed it as a record-tying 20th defense, but the WBA title that Golovkin won in 2010 was that organization's second-tier belt.
Golovkin vs. Martirosyan can be seen on HBO.
Yes, the man who celebrated his 32nd birthday on Tuesday will receive a bumper pay-day for doing the honourable thing by the sport and providing Golovkin with an opponent but some things aren't worth the cash and in GGG he'll face a bear with a sore head. "I've been the champion for nine years". When "Canelo" comes back it is going to be under boxing's biggest spotlight and it behooves Golovkin to be in the ring against him. English WBO champ Billy Joe Saunders has kept the only remaining hardware out of Golovkin's grasp, repeatedly declining Golovkin's challenges.