Brian Norman Jr retained his WBO welterweight world title by stopping Jin Sasaki with one explosive punch in Tokyo.

The American dropped Sasaki twice in the first round and the one-way traffic continued once the challenger rose quickly to his feet.

Sasaki, 23, tried to fight fire with fire in front of his home crowd, but that approach was punished in the fifth when Norman Jr landed a powerful left hook.

The shot put Sasaki out cold and the Japanese fighter was worked on by medics for several minutes, before being taken out of the ring on a stretcher.

It meant Norman Jr stood alone in the ring without his opponent as the official result was read out.

The 24-year-old extended his unbeaten record to 28-0, adding his 22nd knockout and his third stoppage in a row.

The Georgia native is eager to add more world titles to his collection after a knockout of the year contender.

Norman Jr did have his sights set on fighting IBF and WBA champion Jaron ‘Boots’ Ennis, but his domestic rival confirmed this week he intended to move up in weight.

“I wish I had a certain fight coming up,” he said afterwards.

“But they heard B Norman the Storm was coming. Y’all know what happens when a storm’s coming, they grab their boots and run.

“We shall see what’s next for me, hopefully October or November.”

After the bout, Sasaki’s team announced the fighter had undergone a CT scan at hospital and there was no “bleeding” or “injuries or trauma”, but the fighter was suffering from memory loss.