The Birmingham fighter successfully defended his Lonsdale belt to take his professional record to 15-0 with 10 knockouts.
Overwhelming pre-fight favourite Gavin said: "I'm getting better and was pleased with my performance tonight.
"Training wasn't ideal as I injured my left arm during camp and my son Daniel was admitted to hospital with illness last night but I showed my mental strength in there.
"I'm ranked number one for the European title and I'd like to go for that now. I'm ready."
Defeat for Welborn takes him to 11-1, with five KOs.
In other action, local fighter Martin Gethin claimed the vacant British lightweight title, also with a ninth-round stoppage of Hove's Ben Murphy.
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