Cowie, who was bought from Inverness on transfer deadline day, scored the opener and made the second goal at Vicarage Road.
And he is glad he accepted the challenge to play in England, saying: 'I could have stayed in Scotland - but I wanted to better myself and I think I'm doing that here.
On target: Don Cowie scores the opening goal for the hosts at Vicarage Road
'You go into every game here and it's different. 'The challenge is there every week, whereas in Scotland you play every team four times and it gets monotonous.'
Cowie appeared to be offside for his goal, but linesman Paul Martin did not flag and the midfielder latched on to Grzegorz Rasiak's flick and beat Julian Speroni.
And in the second half Cowie wriggled past Matt Lawrence and sent in a low cross which hit Jobi McAnuff before bouncing off Jose Fonte via Speroni in a mess that ended up with the ball in the back of the net.
Out in the cold: Palace keeper Julian Speroni cuts a disconsolate figure as Watford's second scorer Jobi McAnuff is mobbed by his delighted team-mates
Palace have won just one game in their last seven and are 10 points above the drop zone, leaving defender Clint Hill concerned about the prospect of relegation.
He said: 'Of course we still need to be a bit careful - we're not safe yet. We need three wins as quick as possible to get us safe.'