LONDON -- Gennady Golovkin steamrolled to yet another knockout victory to retain his world middleweight title in a slugfest against Kell Brook on Saturday night at the sold-out O2 Arena.

Golovkin, the much heavier puncher, punished Brook before unloading a brutal onslaught of blows against the game welterweight titleholder, sending Brook's trainer, Dominic Ingle, onto the ring apron to throw in the towel in the fifth round.

It was just the kind of fight Golovkin wanted.

"I promised to bring 'Big Drama Show,' like street fight," Golovkin said. "This is not boxing, this is more like street fight. I feel it's finished [in the fifth round]. I feel it's game over."

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 championship.

But Brook (36-1, 25 KOs), who was moving up two weight divisions, was overpowered by perhaps the best puncher in boxing. Brook took some thunderous shots and never went down, but he seemed shaken by the numerous punches Golovkin landed.

Golovkin (36-0, 33 KOs) retained his 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.

Gennady Golovkin, left, defeated Kell Brook by fifth-round TKO for his 23rd straight knockout and his 17th straight title defense. Andrew Couldridge/Reuters

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

But Golovkin took some clean licks before putting Brook away.

"He got hit, but he was definitely the bigger puncher," said K2 Promotions' Tom Loeffler, Golovkin's promoter. "We give Kell Brook a lot of respect. He would probably beat a lot of the middleweights, just not GGG. Gennady came into the lion's den. You saw the atmosphere at the O2, where the U.K. fans were cheering for Brook, but Gennady did his job, retained his titles and kept his knockout streak alive."

Golovkin started quickly, perhaps wanting to see what Brook could take, and he buckled Brook with a hard left hook along the ropes about a minute into the fight. Brook overcame the brief distress and landed some clean shots, but Golovkin did not flinch.

Brook landed several punches throughout the fight, giving the electric crowd false hope, because in addition to Golovkin's power, he also has a granite chin. He has never been knocked down or visibly hurt in his career.

Punch stats Punches Golovkin Brook Landed 133 85 Thrown 301 261 Percent 44% 33% -- Courtesy of CompuBox

"I don't feel his power. I feel his distance," Golovkin said. "He has great distance. He feels [my power], and after second round I understand that it's not boxing. I need street fight. Just broke him. That's it."

Brook used his movement to stay away from Golovkin for stretches in the second round, but still ate a right and a left to the head. Brook responded with a series of head shots that sent the crowd into delirium as he and Golovkin slugged it out briefly in a possible round of the year contender.

Golovkin attacked Brook to open the third round and landed a body shot and straight left that forced him to the ropes. Golovkin also damaged the right side of Brook's face with heavy blows.

Brook went to the hospital after the fight with a broken orbital bone around his eye. He posted on his Twitter account that he would need to have surgery next week.

"I'm devastated. I expected him to be a bigger puncher," Brook said. "I think in the second round, he broke my eye socket. He caught me with a shot, and I was starting to settle into the fight, but I was seeing three or four of him, so it was hard to get through it. I was tricking him. His shots were coming underneath, and I was frustrating him. I was starting to settle into him, but when you see three or four of them, it is hard to carry on.

"Believe me, I hurt him. When you're in a fight, you can see every movement of a fighter, and I saw his legs buckle a couple of times. He's a scary champion. Nobody wants to fight him, but I would fight him again, with a good eye. He is a great champion. I'm trying to give back to the fans, and I hope they enjoyed the fight while it lasted. I wished I could go on, but when there are five of him, you don't know which one to hit."

Golovkin battered Brook in the fifth round, forcing him to the ropes and teeing off. Brook spun away and threw up his hands as if to say, "I'm still here," but it was his last stand.

Golovkin pounded Brook around the ring with both hands and had him trapped in a corner, firing huge rights and a left to the body. In all, Golovkin blitzed Brook with more than a dozen unanswered punches.

"I hope they enjoyed the fight while it lasted. I wished I could go on, but when there are five of him, you don't know which one to hit." Kell Brook, who suffered an eye injury in Saturday's fight

Ingle got on the ring apron and waved a white towel, but referee Marlon Wright did not immediately notice. Golovkin got in a few more monster punches before Wright recognized the corner and waved off the fight at 1 minute, 57 seconds, immediately quieting the frenzied crowd.

"No, this is not a surprise," Golovkin said of the towel being thrown in. "First of all, I respect Kell. Kell is good fighter. He is not middleweight. This is not his division. [Trainer] Abel Sanchez tell me to, 'Just take your time, do not box him. Just pressure him, because he is broken.'

"I respect Kell. He is real, and thanks to his corner, for his career and for his family, [the stoppage was] correct."

Said Ingle, referring to Brook's eye injury: "You can't be fighting a guy like Golovkin when you can't even focus on the guy."

Brook, 30, still had his wits about him when Wright stepped in, and he seemed surprised that his corner called for the stoppage.

"A fight with this magnitude, it should have carried on," Brook said. "Dominic Ingle has seen me probably from 9 years old coming through. He was watching from the outside. I don't know what was going through his mind. But me as a warrior, I wanted to carry on. Knock me out, knock me out."

When it was over Golovkin, 34, a Kazakhstan native fighting out of Santa Monica, California, simply walked back to his corner, showing virtually no emotion as he racked up another knockout.

"The corner did the right thing," Sanchez said. "It was a matter of time. He was taking too many clean shots. At that point when they stopped it, it was over. Gennady knew it was over, and he was touching him with too many clean shots. I think something is wrong with [Brook's] eye, and the heavy hands were going to injure him permanently.

"I noticed it in the second round when he kept pointing to it and kept touching it. [Ingle] did say that something was wrong with his eye. But it wasn't so much with his eye as he was getting hit with too many clean shots. That could be very dangerous."

Many thought that perhaps Golovkin was ill during the week, because he was a bit more reserved and seemed a little irritable, but he said he was fine, dismissing the rumors. And he sure looked healthy as he plowed through Brook, who was hoping to join all-time greats Sugar Ray Robinson and Carmen Basilio as the only reigning welterweight titleholders to win middleweight titles.

Gennady Golovkin said he wants to target a middleweight title unification bout with Billy Joe Saunders next. Reuters/Andrew Couldridge

"I feel great. It's because I'm not smiling. This is serious business," Golovkin said. "I understand my situation in middleweight. I feel after first round that he's not middleweight, and I am not scared."

Sanchez was not overly impressed by Golovkin and assigned him a grade of 4 on a 1-to-10 scale.

"He was trying too hard to knock Kell out," Sanchez said. "The not smiling [Friday at the weigh-in], he had an hour and 40-minute ride [because of traffic]. He was upset and wanted to get on the scale and get out of here. He just was trying too hard. I was trying to tell him this is a 12-round fight. Just beat on him, beat on him, practice. I wanted him to use the jab more. He wasn't. He would use it for half the round and then not use it."

Golovkin plans to return Nov. 26, the date HBO is holding for him. Lineal champion Canelo Alvarez, who fights Liam Smith for a junior middleweight world title on Sept. 17, refuses to fight Golovkin.

Golovkin could face secondary titlist and mandatory challenger Daniel Jacobs, who defended his belt with a seventh-round knockout of Sergio Mora in a rematch on Friday night. After the fight, Jacobs called for the fight with Golovkin.

"We hope a lot of the fighters that turned Gennady down before will not just talk about fighting him now but will actually get in the ring with him after seeing him get hit by Kell Brook," Loeffler said.

Golovkin would also like to win the last belt of the major belts he does not have. It belongs to England's Billy Joe Saunders, who has already blatantly ducked Golovkin. But Golovkin said he holds out hope.

"I'm open for everybody, [but] I want a unification fight," he said. "I would like Billy Joe Saunders first of all, because he has the WBO belt."

Golovkin wants Saunders, and he wants Alvarez, and he wants Jacobs. He wants them all and has been saying it for years.

The question is, who wants GGG?