The Belgium striker came off the bench to score twice in the final 20 minutes of the second half, either side of a header from Cesar Azpilicueta, as the champions came from 2-1 down to seal only a second Premier League win in five games.
The 24-year-old has struggled for form and playing time this term, particularly in the top flight, and Antonio Conte's decision to bring him on in place of Alvaro Morata was met with boos by some Chelsea fans at Stamford Bridge.
Batshuayi admits it has not been easy for him in recent weeks but was thrilled to respond with a telling impact.
"It's been a difficult moment for me but I stay focused, I've been training hard. I scored two goals and it's good for the team," he told Sky Sports.
"I'm very happy to take three points in a difficult moment. Now we have to stay focused."
Calling for Batsman ?— Michy Batshuayi (@mbatshuayi) October 21, 2017
I got yall pic.twitter.com/tFPHP4sFO5
Asked what Conte had told him prior to being introduced in an attempt to change the game, Batshuayi said: "Nothing. Only to fight for every ball with spirit."
The win lifts Chelsea to fourth in the table and ends a run of three consecutive games in all competitions without a victory.
Azpilicueta, whose header completed the Blues' comeback before Batshuayi added a fourth in injury time, was proud of the spirit showed by his side against an excellent Watford team.
"We left it very late, we had to dig in but we showed great spirit," he said.
"It wasn't our best game but we got an important win for our confidence after three games without winning.
"We started really well, we were 1-0 up and we had chances to score the second. The last kick of the first half, we concede a goal, and obviously confidence is a bit low.
"We were three games without winning, we had difficult games at home we were not able to win. We know it's a long season but this is the first step to get our confidence up."