The Hornets, who went into the match seeking a fifth straight win, missed their best chances with the scores level.
But Zola refused to be too harsh on his team, and admits he will be looking for a response when Watford entertain Bolton on Saturday.
"Losing is part of the game," Zola said. "You win and do well like we have been recently and then you play a bad game like this.
"We are not a team who are going to be invincible and will win all the games.
"We were in a good spot and we are going to keep pushing. We know that we need to improve on this, we made some mistakes and we didn't expect them to play in that way.
"That and the lack of quality in the last third has caused the problem.
"I think what is important is the reaction. Saturday we have a big game and I am expecting a good reaction from the players."