The Bluebirds manager watched his side fade markedly after taking the lead in the 26th minute through Mark McGuinness.
The centre-half’s far-post volley from a Joe Ralls corner suggested a comfortable afternoon might be in store for the hosts against a Hornets outfit that had lost their three previous Sky Bet Championship outings.
But while the equaliser from Watford striker Vakoun Bayo arrived after a howler by Cardiff goalkeeper Jak Alnwick, the hosts never did enough to win.
Bulut said: “The first 35 minutes was good, but I don’t know what happened afterwards. We totally changed.
“I don’t know why, whether it was pressure or they were stressed. In the end we have to be happy with one point.
“Perhaps after four wins in a row we thought we were great, but we have to work, and today we didn’t work as a group.
“I am satisfied with the start of the season, but not with today.”
It was a shocking mistake by Alnwick, which left the Cardiff City Stadium stunned.
There appeared no danger when McGuinness played a square pass with his team set to clear their defensive lines.
But Alnwick’s first touch was horrid, the ball bouncing off his boot into the path of Bayo who side-footed into an empty net.
Asked about Alnwick’s howler, Bulut said: “We played too many balls back to the goalkeeper which was not necessary.
“We created the chances for them. When we have the chance to play forward, we must do it. You can use the goalkeeper, but not too much.”
It was no more than Watford deserved, with boss Valerien Ismael insisting his side should have taken all three points.
They improved a lot in the second half, enjoying more possession and creating the better opportunities.
Ismael said: “We should have won, no doubt about that. When a team has lost three games and is low on confidence it is difficult.
“We didn’t trust our own quality. The mentality in the second half was very good and we did not concede any chances.
“We expected more points than we have but we will take it step by step. The goal we conceded was incredible, just too easy. But we kept fighting.”