A frustrated Marco Silva said referee Lee Probert made a " big mistake" by sending off Marvin Zeegelaar as Watford were beaten by Burnley.
Zeegelaar was shown a straight red card in the 39th minute of the clash at Turf Moor for a two-footed tackle on Steven Defour.
Scott Arfield soon made the advantage count by scoring the only goal of the game just before half-time, and Watford could not recover in the second half despite a spirited showing.
Silva, who was animated on the sideline throughout and spoke to referee Lee Probert at half-time and full-time, told Sky Sports the result was "not fair".
"We came here to play. We started very well, created the first big chance to score, and after 20-25 minutes Burnley started to balance the match more," Silva said.
"There was a good competition between everybody, then after one decision the referee made a big difference in the match, a big influence, and it was a harsh decision for me. It's not a red, that changed everything, and after two or three minutes they scored.
"In the second half, even with 10 players, we created chances to score and I didn't think Burnley once had the game under control. Every moment we had the ball and started to organise our attack we create chances. It's not a fair result and our players didn't deserve what has happened this afternoon."
Watford also had a couple of penalty appeals turned away and Silva appeared annoyed that Phil Bardsley was only shown a yellow card for a late tackle on Richarlison.
"The referee never had control of the match and he lost it with the moment when he made the mistake," said Silva. "I understand I can make mistakes and so can our players, and the referee can too, but he made a big mistake and that had a big influence."
Despite the defeat, Silva said there were positives to take from the game.
"We took good things from the match. We showed big attitude and commitment again and I saw moments of quality with 10 men which is very good, but we go home with zero points which is not fair. Even with 10 we competed until the end, I am sure with 11 we would take a good result."