Wales international Boaz Myhill says his work with Birmingham goalkeeping coach Watson - the man Hart says transformed his fortunes when he lost his Manchester City place to Shay Given - is a big part of the reason.
Myhill, 28, aims for his fifth clean sheet of the campaign at Southampton today, and he said: "The training here has been excellent - far more physical than I have been used to in the past.
"But I've really enjoyed it and I'm confident Dave is going to improve me. I'd say we're very lucky as a Championship club to have a goalkeeping coach of that quality. Everybody saw how Joe improved during the season he spent at this club."