Koeman spent heavily during the summer, but over the 90 minutes they were no match for Spurs, who took the points courtesy of a Harry Kane brace and Christian Eriksen strike.
Asked about Everton's aspirations of joining Tottenham as a top-six club and what the game showed in terms of how far away they are, Koeman said it is unfair to judge as the Toffees are a newly formed side.
"If you look at the second half, we are really far away," he said. "If you look at the first 30 minutes, it is different.
"But the difference between Everton and Tottenham is that they have worked a long time together now with the same players and it is not realistic to expect that Everton already is at that level.
"If you think we need to be at that level, then it will be really difficult."
Regarding the disappointing performance, the Dutchman suggested the Toffees had initially been a match for their opponents before rapidly suffering in terms of confidence when the goals went in.