The away side mounted a late comeback to win 2-1 at Vicarage Road, in what will be a tough loss to take for the Hornets.
Andre Carrillo opened the scoring for the hosts, nodding home on the rebound from Richarlison’s effort but goals from Jordan Ayew and Luciano Narsingh sealed all three points for the visitors.
Should have won
Speaking to the gathered press after the game, Silva said: "It’s our job to find out why we cannot kill games off. It’s clear, we have to put the ball in the net.
"We made enough chances,” the Portuguese manager admitted, “the game was under control and the opponent didn’t create chances to put us in danger until then. We needed to score a second goal. We needed to be assertive."
"I'm very disappointed for us. I’m disappointed for our fans as well.”
Before Swansea’s two goals, Watford only outshot Swansea by one, but they did create the much better chances.
Andre Gray had a golden chance to seal the win for Watford, the substitute was clean on goal but goalkeeper Lukasz Fabianski was equal to his close-range effort.
Silva continued: "We did enough to win the game, our opponent had one shot on target from Ayew, but after that they didn’t create a chance until they equalised.
"Heurelho Gomes didn’t make a save until then,” although Swansea did have two shots on target before the goals, neither troubled the goalkeeper, “and we had enough chances to win the game and kill it off.
"We had a clear chance just before then, and at this level when you don’t score it gives the opponent some belief.
"We didn’t create a big number but there were enough.” Although Swansea did outscore Watford in Expected Goals (1.44 to 1.22) [via Infogol] the away side’s only big chances were the two late goals. “They won a second ball, and even after that we needed to keep focused.
"It’s a big mistake, our players didn’t stay focused until the end and we were not in position."
Watford next face a difficult trip to the Etihad Stadium to face the champions-elect Manchester City before facing Bristol City in the FA Cup at home.