By Declan Taylor

O2 Arena, London - IBF/IBO/WBA/WBC middleweight champion Gennady 'GGG' Golovkin (36-0, 33KOs) was tested, but battled back to stop IBF welterweight champion Kell 'Special K' Brook (36-1, 25KOs) in five rounds. Brook's corner threw in the towel when their fighter appeared to be in trouble in the round.

Brook, who fights at 147-pounds, moved up by thirteen pounds to face Golovkin at the full middleweight limit of 160-pounds.

When the first bell rang, they came out jabbing with Golovkin stalking and looking to land something big. Brook was doing well to stay away from danger and was managing to stay out of danger for the most part. But towards the end of the round Brook appeared to get rocked by Golovkin hook to the body and held on to prevent further damage. Brook came roaring back with a good combination of punches in the closing moments to get the crowd on their feet.

Golovkin went back to stalking at the start of round two. Brook's faster hands were getting to Golovkin hitting the target first. Golovkin was very active with the jab, using it was the objective of landing something big. Brook was on the move, stalking being defensive and looking to counter. Brook nailed Golovkin was a huge uppercut and then landed a variety of punches to rattle the champion's head back - with the entire arena erupting to their feet.

Golovkin went after Brook at the start of round three. He was coming after Brook like a madman and throwing heavy shots with both hands. Brook was using his movement and trying to avoid a lot of the incoming danger. Golovkin was applying a lot of pressure, looking to sap Brook of his energy. Brook once again came back in the final minute, landing a big variety of punches as Golovkin seemed to be hurt for a moment.

At the start of the fourth, Brook's face was starting to swell up. Golovkin was pressing forward, using his jab to get inside. Brook was moving around and looking to weather the storm and Golovkin's pressure was heavy and he was throwing a lot of leather. Brook landed a few good shots at the end.

Brook's nose was steadily bleeding at the start of the fifth. Golovkin was unloading on Brook at the start of the round. He was landing a few of those punches, but missing many as well. Golovkin continued to unload and Brook was not throwing anything back, which prompting Brook's corner to throw in the towel. Brook did not seem to be in a lot of trouble when the towel came in and caught everyone by surprise.