Round-by-round: Gennady Golovkin stops Kell Brook by 5th-round stoppage

Middleweight champion Gennady Golovkin took some hard shots in the first few rounds from England's Kell Brook. But in the end, Golovkin's vaunted power was too much for the British fighter who had moved up two weight classes to challenge the fighter known as Triple G.

Golovkin stalked the undefeated welterweight champion - fighting at middleweight for the first time - almost from the opening bell at the O2 Arena in London and won by 5th-round TKO when Brook's trainer Dominic Ingle threw in the towel, feeling his fighter was absorbing too much punishment. It was Golovkin's 23rd consecutive knockout victory.

Golovkin (36-0, 33 KOs) retained the two major belts he had sanctioned for the fight. Brook (36-1, 25 KOs), had a strong second round, but after that it was pretty much all Golovkin, Paste BN/Boxing junkie's No. 2-ranked pound-for-pound fighter in the world.

Here's a round-by-round analysis of the fight:

Round 1: Golovkin charges in with a left early in the round that misses. He's not wasting time going after Brook. Throws a few left jabs, GGG gets Brook on the ropes and hurts the former welterweight. Brook gets his legs back under him. Golovkin cutting off the ring nicely. Both connect with right hands at the same time as the round ends. Golovkin wins the round.

Round 2: GGG comes out swinging again. Brook throws some nice combinations that don't seem to hurt GGG. Then lands a few jabs. GGG throws combos of his own and seems to be looking to end this early with some wild rights and lefts that miss. Brook now taking it to GGG, boxing superbly and cutting GGG on the forehead. Brook's round 1-1.

Round 3: Brook goes down early but referee Marlon Wright calls it a slip. Hard left by Brook lands, followed by a hard right by GGG. Lots of action here. GGG barely misses with a right and Brook comes back with hard combinations as the crowd roars. Lots of action hear the end of the round as Brook ends with a flurry. I give the close round to GGG 2-1.

Round 4: Brook throwing combinations and exciting the crowd. GGG having a tough time connecting with some wild rights. Brook withstanding GGG's punches very well. Hard right by GGG connects. Definitely the toughest fight GGG has been in that I've seen. Give the round to GGG 3-1.

Round 5: GGG comes out firing again. Backing Brook up now. Hard right snaps Brook's head back. GGG going in for the kill now and punishing Brook. And Brook's trainer Dominic Ingle amazingly throws in the towel. This one's over! Golovkin wins by 5th round TKO. Wow. What a quick ending. Thought Brook still had something left.

(Photo of referee stopping the Golovkin-Brook fight when Brook's corner threw in the towel for a fifth-round stoppage by Richard Heathcote, Getty Images)