The clash between unbeaten domestic fighters started brightly for Gavin, who used superior footwork and swift movements to land from range in the first three rounds.
Vassell applied pressure in the fourth but was caught cleanly on more than one occasion, with Gavin landing at will with an accurate southpaw jab.
Round five looked to have turned the tide slightly for Vassell as the Manchester native caught his man against the ropes, landing a heavy shot with venom for the first time.
Gavin quickly recovered though, targeting a swollen jaw that continued to trouble his opponent throughout the sixth round.
After seven rounds the doctor was called to examine Vassell's jaw, with the decision made that he was no longer fit to continue.
An impressive victory for Gavin moves the former world amateur champion to 16-0 as a professional, with 12 of those wins coming via stoppage.