The Hornets boss watched his team take a 2-0 lead following fine strikes by Javier Acuna and Davide Faraoni either side of half-time.
But summer signing Gary Hooper, who made his long-awaited debut for Norwich from the bench in Saturday's 1-0 loss to Aston Villa, took the game to extra time with a header deep into injury time after Josh Murphy had pulled a goal back.
Former Celtic striker Hooper then sealed the win for the Canaries when he slotted home Leroy Fer's tremendous pass with just five minutes of extra-time remaining.
'It is a crushing feeling of course," said Zola.
"We were winning a game and deserving to against Premier League opposition. But this game is about the attention you put in at crucial moments and that is the learning side for us."