The Hornets impressed as they continuously caused Antonio Conte's men problems with a dazzling attacking performance.
Speaking to BBC Sport after the game, Garcia said: "It was an unforgettable night. A great victory and a great match. I am very proud of my players today."
Watford had dominated from the start and when the visitors went down to ten men on 30 minutes, after Tiemoue Bakayoko was shown a second yellow, this will have given the home side even more belief that they could go on and win the game.
"You always try to look for the victory and play well. Today we played a good match, pressed high. OK, the match changed after the sending off but I think we played very well," said Gracia.
"Chelsea are a very big club, a big team. Today they had more difficulty because of the sending off but there was in the second half moments when they played better."
Gracia acknowledged the win as a massive victory but he already has his mind on the next game.
"I only think to get the next three points. Tomorrow we start training again to be ready for the next match," said the Spanish manager.
(You may also be interested in 'Watford 4-1 Chelsea: Hornets Breeze Past 10-Man Blues With a Dominant Display at Vicarage Road')