Gennady Golovkin wins after Kell Brook's corner throws in towel

— -- LONDON -- The GGG knockout streak continues.

Gennady Golovkin, the much heavier puncher, punished Kell Brook for nearly five rounds before unloading a brutal onslaught of blows against the game welterweight titleholder. That sent Brook's trainer, Dominic Ingle, onto the ring apron to throw in the towel in the fifth round Saturday night at the sold-out O2 Arena.

Brook said afterward that his vision was affected after he suffered a broken eye socket in the second round.

"I am gutted, because there was much, much more to come from me," said Brook, who was taken to the hospital after the fight. "I was just getting started, but I was seeing five of them out there. I think I have busted an eye socket."

Golovkin praised Brook but said he never felt like he was in danger.

"I respect him. He's good but not so strong," Golovkin said. "He just touched, but I didn't feel his power. So many punches, but I didn't feel them."

Brook's home-country crowd had come to see if he could pull off one of the biggest upsets in British boxing history, a list that includes Randy Turpin's 15-round decision against Sugar Ray Robinson to win the middleweight title in 1951, Ricky Hatton's 11th-round knockout of Kostya Tszyu to win the junior welterweight title in 2005, and Tyson Fury's decision win over Wladimir Klitschko 10 months ago to win the heavyweight title.

But Brook (36-1, 25 KOs) was overpowered by perhaps the best puncher in boxing. Brook took some thunderous punches and never went down, but he seemed shaken by many of the punches Golovkin landed.

"I expected him to be a bigger puncher," Brook said. "In the second round he broke my eye socket, but I was tricking him, I was frustrating him. I was starting to settle into it, but when you see three, four, five of them it's difficult.

"I hurt him. When you're in the fight you can see, his legs buckled a little .... I would fight him again, with a good eye."

Golovkin (36-0, 33 KOs) retained his middleweight?title for the 17th consecutive time. The middleweight division record is 20 straight defenses, set by the great Bernard Hopkins, who was ringside as an HBO analyst.

Golovkin said he would like to target a unification fight next with Billy Joe Saunders.

"I'm open for everybody," Golovkin said.

Golovkin, who has not gone the distance since winning an eight-round decision in 2008, notched his 23rd knockout in a row and increased his division-record knockout percentage for middleweight title fights to .917.

The Associated Press contributed to this report.