Hakim Ziyech struck the winner as Chelsea stayed top of the Premier League, but demanding Tuchel was not impressed by his side's performance.
"That’s not us," the German told Amazon Prime. "We were absolutely not ready today for this match. I missed maybe to find the right approach to make my team ready. We did not cope with the pressure, with the first ball, second ball.
“We had a lot of changes but too many faults. It did not get better. The only thing we could do was hang in there and focus on the easy things. It was a lucky win.
"I see this totally as an exception from the rule. I will not insist too long on this match because it’s so unusual for us to play like this."
He did reserve praise for one of his star names, as he believes Kai Havertz is coming to the boil after a classy display.
"Havertz was very strong today," he added. "I felt he was the one player reaching his level today.
"We missed some players. We had some players overloaded. We stole three points. We don’t have to talk around it. For the first time it feels like a lucky win.
"We were not ready for this game. We are to blame. We never found the right attitude. It was a big exception from the rule. We never found the minutes. It got a bit better in the second half. We conceded a lot of chances in first half and did not create much. The two situations we had, we scored. We were very lucky to escape with the win.
"Maybe I didn't find the right approach. It felt like we were not ready for the long balls, the pressure. When we won the ball, how to escape out of the pressure. We had big problems individually and as a team. We never felt solid. It felt like we were never in control.
"We need a lot of points if we want to stay in title race. We felt like we lost two points against Burnley and Manchester United. We stole minimum two, maybe three back today. It feels like today we showed when we scored some quality.
"Overall we can do much better. There are some reasons - we have injured players and some key players due to overload were not on the pitch. I don’t want to be too critical. Watford deserved more."
A Watford fan suffered a cardiac arrest in the Graham Taylor Stand 12 minutes into the match at Vicarage Road and referee David Coote took both sets of players off the pitch.
Medical staff from both teams raced across the pitch to assist the supporter, who was stabilised and then carried out on a stretcher to be taken to hospital.
When the match resumed it was Chelsea who took the lead, with Mason Mount stroking the ball past Daniel Bachmann in the 30th minute.
However, the visitors’ advantage did not last long and Emmanuel Dennis, who had been a doubt for the fixture, struck the ball into the bottom corner.
In the second half, substitute Ziyech fired past Bachmann from a Mount pass to secure all three points for Chelsea.