Villa were 1-0 down and comfortably second best after the first half of Saturday’s match at Stamford Bridge.
But with players expecting Emery to be angry, he instead delivered a positive half-time message before making the changes which helped transform the match in his team’s favour.
Watkins was brought off the bench just before the hour mark and scored twice as Villa claimed an 11th straight win to equal a 128-year-old club record.
He said: “Chelsea were very good in the first half but at the break the manager was so calm.
“In games where you think he is going to shout at us and get on to us, he is the opposite.
“In games where we think we have done well he ends up getting on to you and demands more.