Borussia Dortmund suffered a shock 2-1 loss to visitors Cologne on Saturday to drop four points off the pace in the Bundesliga title race.
Cologne stunned Dortmund with an early goal when Ellyes Skhiri tapped in at the far post in the ninth minute.
Dortmund, who had fired five goals past Hertha Berlin last week, were lacking any punch and instead it was hard-working Cologne who scored again with Tunisia international Skhiri on the hour.
Thorgan Hazard cut the deficit with a low shot in the 74th minute but despite desperate late attacks and a golden chance missed by Erling Haaland deep in stoppage time they could not get an equaliser.
Dortmund are third on 18 points, four off leaders Bayern Munich and two behind RB Leipzig.