Borussia Dortmund boss Thomas Tuchel admitted that his side were not at their free-flowing best in Saturday's 2-1 victory over Mainz.
Pierre-Emerick Aubameyang scored both of his side's goals at Signal Iduna Park, with substitute Yoshinori Muto pulling one back for the visitors in stoppage-time.
The victory extended Dortmund's incredible unbeaten home run that dates back to April 2015, but Tuchel felt that his charges looked laboured at times on what was an extremely hot afternoon.
"Today we might have been an attacking and passing machine, but we were not a proper machine," he said. "That's not meant as an accusation, but more of a description.
"We looked nervous to some extent, did not find the right structure and did not find the spaces behind Mainz's first line of defence.
"On the occasions we did find them, then we had difficulties getting our combination play going.
"It looked a little bit dogged. It was an arduous victory.
"In the second half we defended the counter-attacks well. We sank our teeth into the game and always kept our heads up.
"The result is important, above all because we didn't play our best on the day."
Dortmund return to action next Saturday when they visit newly promoted Leipzig.