Victory against the unfancied Ecuadorians, who lost both their opening games, would have taken Croatia through to the second round.
But they turned in a lacklustre performance and went down to a lone strike from Edison Mendez.
"At half-time the players were aware that something was lacking in the rhythm," Jozic said. "Of course they were nervous.
The plan was to push up and put pressure on them - I don't know what happened
"We had three or four good chances in the second-half but we didn't take them because they couldn't concentrate.
"Ecuador could see that and they just took control of the game.
"I wouldn't categorically say the players were too stressed out, but I noticed individuals in our team who were having problems, particularly in the second half."
Jozic said his side did not follow the tactical plan he had laid out for them before the match.
"The plan was to push up and play 30 metres from our goal and put pressure on them," he said. "I don't know what happened.
"Our back line drew back deep in the first half and our midfield followed them.
"They had an agreement that the defence would push up. But when they started going forward they lacked concentration."