The reigning Serie A champions scored three goals in the opening 20 minutes as they brushed aside Roma by four goals to one in in impressive display.
Zeman told reporters at the post-match press conference that the manner of defeat was disappointing.
He said: "Roma are improving, but this game was terrible, Juventus were superior throughout.
"We neither attacked nor defended effectively, and so were constantly under pressure. Tonight, I saw very little of what we do during training, although we are still a work in progress.
"Conceding three goals rapidly would have knocked any team out. I hope the players realise they were too sluggish tonight, and didn't do enough."
An inconsistent start to Serie A sees Roma lie in 8th place in the standings after six matches.