Goalkeeper Marwin Hitz made an embarrassing error on Saturday as Borussia Dortmund's Champions League qualification hopes suffered a blow with a 2-1 loss at Freiburg in the Bundesliga.
Hitz fumbled Jonathan Schmid's second-half shot to hand Freiburg their first win against Dortmund since 2010. The defeat left Dortmund three points and two places adrift of the top four.
"We need to turn results around quickly. I don't want to imagine not playing in Europe next season," Dortmund midfielder Emre Can told Sky.
"I'm not just disappointed, I'm annoyed. We made mistakes again today which we can't afford to make," said coach Edin Terzic.
A long-range effort from South Korean youth international Jeong Woo-yeong gave Freiburg the lead just after half-time, before Hitz allowed Schmid's shot to slip through his fingers at the near post minutes later.
A late strike from 16-year-old Youssoufa Moukoko was not enough to rescue a point for Dortmund.
Elsewhere, former Arsenal defender Shkodran Mustafi endured a difficult debut for Schalke as a 3-0 defeat at home to RB Leipzig kept his new club rooted to the bottom of the table.
"Of course I'd hoped for a better debut. I knew it wasn't going to be easy here, but I think there is still hope," said Mustafi, whose side are nine points adrift of safety.
Nordi Mukiele gave Leipzig the lead at the end of a turgid first half, beating Mustafi in the air to head the ball in at a corner.
Marcel Sabitzer put the game beyond doubt in the second half, sweeping a low shot past Mustafi and goalkeeper Ralf Faehrmann, before Willi Orban headed in Leipzig's third.
The win kept second-placed Leipzig seven points behind league leaders Bayern Munich, who had temporarily extended the lead to ten with their 1-0 win at Hertha Berlin on Friday.
Both Wolfsburg and Bayer Leverkusen remained hot on Leipzig's heels with wins on Saturday.
Second-half goals from Wout Weghorst and Ridle Baku gave Wolfsburg their fifth win in a row away to Augsburg, while Leverkusen were 5-2 home winners in an entertaining clash with Stuttgart.
Kerem Demirbay put Leverkusen in front with a neat backheel volley from close range on 18 minutes and nutmegged Stuttgart goalkeeper Gregor Kobel to double the lead shortly afterwards.
Sasa Kalajdzic struck twice in the second half, but his second was a mere consolation goal. Leon Bailey and Florian Wirtz had already given Leverkusen a commanding lead.
English winger Demarai Gray, who joined Leverkusen from Leicester City in January, added a fifth before full-time on his debut to pick up his first Bundesliga goal.
Elsewhere, second-from-bottom Mainz moved to within four points of safety as Moussa Niakhate's first-half penalty gave them a hard-fought 1-0 win at home to Union Berlin.