Olympic champion Campbell initially pulled out of the fight because of the ill health of his father, but with the blessing of his family he made a late decision to return to the bill.
The 27-year-old lightweight maintained his perfect professional record, extending it to 11 wins, putting his Nicaraguan opponent down at the end of the second and then again at the start of the third.
That was enough for referee Howard Foster, whose decision to call the fight off came at the same time a white towel appeared from Morales’ corner.
“I’ve turned the negatives into positives, and I was excited to be here tonight, making my family proud,” Campbell told Sky Sports 1.
“It was a family decision to fight, to give everyone something to look forward to. There’s nothing better for me than boxing in Hull, the love I get is priceless.
“It was very difficult. I pulled out of the show for quite a while. I never intended to box on this show
“My dad will be watching at home as proud as punch. I love you dad, keep fighting.”