Gennady Golovkin retained his WBC and IBF middleweight titles after overcoming Kell Brook's stunningly daring high-wire act in five remarkable rounds at the O2 Arena.

Brook, who remains the IBF welterweight champion despite going down to a first career loss, stepped up two divisions to face the sport's most fearsome operator in Golovkin.

The 34-year-old Kazakh, now in possession of a remarkable record of 36 wins from 36 fights and 33 inside the distance, eventually stalked and pounded Brook to a standstill in round five as the Sheffield fighter's corner frantically waved a white towel.

Speaking after the fight, Brook said he believed Golovkin broke his eye socket during a barnstorming second round and his bloodied features told their own story when the end came after one minute and 57 seconds of the fifth.

Golovkin once again professed his desire to fight Mexican star Saul "Canelo" Alvarez and he remains on course for the superfight the sport desires above all others, although he did not have things all his own way in London.