By Alan Baldwin
Sprott, a 35-year-old former British and Commonwealth champion who had beaten Harrison in 2007, was given an oxygen mask before recovering enough to sag in his corner at London's Alexandra Palace.
"It feels absolutely great," said Harrison, who fought southpaw from the second of the 12 rounds after locking his shoulder and has won 27 fights with four defeats.
"I just had to switch and I was ineffective on that side because I never trained on that side, never fought on that side, but I said losing wasn't an option. I had to find it some way, somehow," he told Sky television.
Derided as 'Fraudley' and 'Audrey' in the past for limp-wristed and lackluster performances, the towering Harrison was booed at times by a crowd clearly behind his plucky opponent.
"I definitely proved that I want to remain in boxing," he said.
"With one hand really I found a shot that made me a European champion, gave me a top 10 rating in the WBC."
(Editing by Ken Ferris)