Borussia Dortmund coach Peter Bosz said his side's 2-1 victory over Augsburg on Saturday was the worst performance of his tenure so far.
Dortmund took the lead after three minutes as Andrey Yarmolenko poked home a loose ball in the box with a swift back-heel, but the lead lasted for only seven minutes before Caiuby headed an equaliser.
Shinji Kagawa scored the winner in the 23rd minute with an audacious chip from just inside the box but, despite the quality of their goals, BVB were far from their best, allowing the match to become an open contest against a physical Augsburg side.
Bosz, who replaced Thomas Tuchel in the summer, told his postmatch news conference: "This was the worst match since I've been the coach at Dortmund. It was never easy today.
"In the first half we found a lot of space but couldn't capitalise because we weren't playing well enough. In the second half, we stopped playing football altogether. Each team has two of those games per season, which is why I'm very happy that we won today."
Dortmund were awarded a penalty in the 79th minute but Pierre-Emerick Aubameyang's attempt at a Panenka was saved by Augsburg goalkeeper Marwin Hitz, capping a disappointing overall display for the striker
"Auba is an important player for us," Bosz said. "He has already scored eight goals. He has always helped us. Today, he didn't play well. One-on-one, header, penalty -- usually he converts them into goals.
"He also has two games per season where things aren't working out for him. Today was his first one."
Asked why he left Mario Gotze out of the squad against Augsburg, Bosz said: "He is not injured. Mario wanted to play but I told him that I didn't want that today.
"He was out for five months and we are nursing him back to form carefully. First he got to play 45 minutes, then 60. Today it would have been his third match within a week. That would have been too much. It was an important game today but there are more vital games ahead for which we need him."
Dortmund enter the upcoming international break on top of the Bundesliga after seven matchdays, keeping the pressure up on their rivals.
BVB keeper Roman Burki told the club's video channel: "It's an extremely important win for us. Those are the games you have to come out on top if you want to win something at the end of the season."
Dortmund went into the game on the back of seven games in 21 days, and Burki said playing in the schedule more familiar to English clubs had been difficult.
"The englische Wochen [English weeks] took a toll on us," Burki told Sky after the match. "You could see that today -- especially in the second half.
"The coach told us ahead of the game that we must show the mentality to win this match at all cost. We battled hard and we won. We weren't always focused, though, giving the ball away cheaply or just lumping it forward. Because of that the match got really tough for us. Augsburg pressed enormously well.
"The table reads nicely but it's still too early for it to indicate anything. Games like today's, in which you have to fight and overcome the tiredness, are the important games."