Zola praised the way his players carved out their opening-day success and paid credit to his striker Troy Deeney for his top-quality goal.
Deeney demonstrated his lethal finishing skill in style when he notched Watford's 11th-minute winner.
Deeney, who scored 20 goals last season, played a silky one-two with Fernando Forestieri before guiding a low right-footed shot to the left of Darren Randolph into the far corner of the net.
It was a clinical goal and highlights Deeney's value to the high-performing Watford side.
In the closing stages of the game it was Watford's defence which had to pull out all the stops as Birmingham surged forward in a desperate bid to grab the equaliser.
Zola said: "I am pleased with the win. It was a tough test to start the season. This is why I am pleased with result and the performance.
"In first half we were excellent for long spells. Perhaps we should have tried to have taken more chances and scored more than one goal.
"Birmingham came back stronger in the second half. We dropped a little bit physically and we allowed them to cause us a lot of problems.
"We demonstrated we are working really well, particularly in the defence. I am looking forward to see a lot more of this kind of play during the season.
"I thought we were good to watch and attacked the space instead of holding the ball.
"But the application was excellent and I am looking to see it more and more during the season."
Zola admitted that there was no need for him to motivate the players after the disappointment of play-off defeat last season.
He said: "Everyone feels we are better prepared as we have more knowledge of the difficulties and we are looking forward making a strong challenge.
"There are some good teams in the Championship and it will not be easy. But our attitude is very good and I thought Deeney took his goal exceptionally well.
"His combination with Forestieri was good. In some spells they were outstanding.
"We believe if we are to make the top flight we have to be well prepared. But I do think we now have a stronger team than lastly season."
Birmingham boss Clark admitted he was frustrated for his players.
He said: "I don't think the players got what they deserved. The supporters have seen the energy, determination and desire in the group.
"The only difference was the quality goal by Deeney from their point of view.
"It was a typical Watford goal - a great bit of movement and a terrific finish by Deeney.
"I've told the players that there is no need to change anything. On another day we would have got at least a draw.
"We didn't deserve to lose against a terrific team who will be there again at the end of the season because of the pace they play at.
"I believe we have hit the ground running and been unfortunate in terms of the result. We just didn't get that little bit of luck.
"We started the game well but they hit us with a quality goal and finished the match on a high note.
"I thought it was a proper home performance in giving the Birmingham fans pride in their jersey."