Watson suffered his second career defeat in his hometown live on Sky Sports when a relentless Crolla dominated the centre of the ring and with it the judges scorecards before forcing a painful TKO victory in the ninth round.
After a run of 13 straight victories, Watson has now lost his last two - both by stoppage - and he admits that making the 9st 9lbs championship limit left him feeling tired and lethargic.
The 27-year-old, who was halted in 11 rounds by Gavin Rees in his first shot at the Lonsdale Belt in November, said: "I've only made the lightweight championship limit three times and I guess my body is telling me my future lies at 10 stone. When I beat Martin Gethin in the eliminator I seemed to tire late in the fight but my fitness got me through.
"Then against Rees I had made the weight a month before when I was a reserve to step in when John Murray was doubtful for his European title fight with [Andriy] Kudryavtsev so I had a good eight weeks or so to make the weight. But for this fight I just didn't have enough time.
| John Watson has vowed to return after his setback British title defeat to Anthony Crolla |
"But I had nothing in me once the bell went. My feet were so heavy and I wasn't anywhere near as sharp as I have been. It was a painful experience."
For all his own problems however, Watson admits that he never underestimated Crolla for a second and he was more than aware that the Mancunian was capable of that kind of performance.
He adds: "I totally respected Anthony Crolla long before we shared a ring. He's a very good boxer and he's fighting out of what in my opinion is the best camp in the country right now. They leave no stone unturned at Gallagher's Gym and he deserved the victory.
"I wasn't surprised by his power, his confidence or his fitness because he's a dedicated kid and a true professional. I just wish that I too would of been at my best because I think it would of definitely been a fight of the year contender.
"So I want to congratulate Crolla, a worthy champion, but also state that I will be back. Undoubtedly that will be up at 10 stone, but I'll learn from this and come back stronger."
NICK PEET