Udinese loanee Matej Vydra scored twice as the former Chelsea striker watched his youngsters seal an impressive win and it left Zola full of praise for the club's academy staff.
Zola told the Watford Observer: "I was delighted. They played even beyond my expectations. We scored two high-quality goals.
"The performance of these young players reinforced in me the conviction I had that whoever worked with these players before in the academy has done a very good job."
Watford begin their Championship campaign against Crystal Palace.