Goals from Keane Lewis-Potter, Vitaly Janelt and Michael Kayode saw Keith Andrews' side brush aside a Tottenham team assembled at a cost of more than £300 million this summer, with the hosts dominant from kick-off at the Gtech Community Stadium.
De Zerbi did not shy away from the scale of the problem, telling BBC Match of the Day: "Bad game. We lost and suffered the difference in the duels. It was the key of this game. We didn't fight in the right way. Maybe credit to them because it's the best quality Brentford have."
The Italian pointed to a squad still finding its feet physically after heavy summer recruitment, with several new arrivals thrown straight into the XI.
"Our physical condition was not at the right level for all players because many came later after the World Cup and there were many new players in the squad and first XI. Marcos Senesi, Jan Paul van Hecke and Sandro Tonali are not in the best physical condition. We knew that before the game."
He conceded the result caught him off guard and refused to hide behind his squad.
"I am surprised by the result and performance. I knew we were not in the right condition. We can't find an excuse. I am sorry for the result and performance. I don't want the excuse that the first XI was not enough to compete and get a result. Brentford's spirit on the pitch was great, it has to be the right example for us."
Lewis-Potter, who opened the scoring inside the first quarter of an hour, described the emotion of delivering for the home crowd.
"It's everything we dreamt of, we have been working so hard in pre-season. We want to make our stadium a ground where it's so hard to play for away teams. We have a special connection and it definitely shows."
He added: "If we get one, we want to get two, three, four and keep on going. We don't want to sit back, that's not in our DNA. We have so much depth now, it helps us a lot."
Brentford boss Andrews, speaking to Sky Sports, admitted he had been unsure what to expect but was thrilled with the response.
"You never truly know where the opposition are at the start of the season. I am really happy with what we produced today. It was us from the first whistle. It was intensive, relentless and filled with a way of playing that is difficult to play against."
He singled out record signing Mamadou Sangare, heavily involved in the build-up to the opener.
"He is a top player, no doubt about it. He is the one we were after in the window. Club deserve a lot of credit. When you bring in a really good player, it brings the level of the team up. But that is not to underestimate what we already had."
Andrews played down any talk of getting carried away: "I am just comfortable where we are in our journey. There are going to be bumps on the road. The plan is to get better. We need to keep pushing and keep striving."