Klopp demands Dortmund improvement
The hosts had coasted through much of the match after rocketing into an early lead through Marco Reus, but looked to have let two points slip when Theodor Gebre Selassie netted a 75th-minute equaliser.
Mario Gotze rose from the bench to bag a late winner, but Klopp said his troops showed they were unfit after 14 weeks without a league match.
"I was pleased with some things, but dissatisfied with others," he told ARD.
"We have had no real match for over three months, which is why I'm pleased."
Mats Hummels also felt his team-mates were slightly sluggish after a long break, and reminded them an opening day win last season did not spare them a flop in form shortly after.
"The result was good, but I am not happy with the manner. The most important thing is to earn three points. Last year we had a great start and after that we had five very poor games," Hummels said.
"Maybe it is better to know that we still have work to do."
Reus netted his first Bundesliga goal for his new club since moving to Signal Iduna Park from Borussia Moenchengladbach in the summer, and the German international was delighted to have made an impact.
"This was my chance and I really wanted to score. It was really important for the team," Reus said.
"Everybody knows that you have to run a lot for Dortmund, but I like doing that."
Match-winner Gotze spoke of his joy at making a vital contribution after a frustrating few months of injuries for the 20-year-old.
"That goal was so important for me. It was such a relief," Gotze said.