Harrison withstood a fast start from Gary Thornhill before digging home a ripping left hook to the ribs which sent the challenger to the canvas.

Thornhill rose, still hurt and was halted after 31 seconds of round five.

It was a calculated performance by Harrison, voted as the best young boxer of the year by the British writers, steadily increasing his accuracy before the sudden finish.

Thornhill threw plenty of leather, but Harrison's counter-punching began to take effect in round three.

Harrison, 24, landed a perfect uppercut in the fourth and kept jabbing well and to find Thornhill's body.

After imposing himself through the fourth, he finished the job with precision.

Harrison said: "I expected him to start quickly. It is the way he fights - he is strong and kept coming.

"We've been working in the gym for that, also on landing body shots."

Promoter Frank Warren added: "It was an excellent performance, and Scott will get better and better."