Eintracht Frankfurt overcame the pre-match loss of in-form Omar Marmoush to beat Borussia Dortmund 2-0 at home on Friday, heaping more misery on the slumping visitors.
Frankfurt, who were forced to cut the Manchester City-bound Marmoush from the matchday squad just hours before kickoff, were clinical and controlled.
Striker Hugo Ekitike put Frankfurt in front early and Dortmund had few clear chances despite dominating control of the ball.
Oscar Hojlund took advantage of a Dortmund mistake in midfield, winning possession and running 40 metres to slide the ball past a helpless Gregor Kobel.
The result means Dortmund, who played in the Champions League final in June, have lost their past three and have just one victory in their last six games.
Dortmund could fall to as low as 11th depending on results this weekend and are 11 points behind Frankfurt, who are on course for their first top-four finish in three decades.
Just hours before kick-off, Frankfurt's sporting director Markus Kroesche confirmed Marmoush had been left out of the squad due to a "very, very likely" move to Manchester City.
Dortmund's preparation was also less than ideal, amid rumours the club's worst season start in a decade had coach Nuri Sahin facing the sack.
The visitors started strong, Serhou Guirassy heading a lofted Julian Ryerson cross against the post eight minutes in.
Expected to carry a heavier burden after Marmoush's departure, Frankfurt's French forward Ekitike put the hosts in front 18 minutes in.
Taking advantage of some sleepy Dortmund defence, Rasmus Kristensen ran into acres of space on the right. The Dane tore down the flank and laid a controlled cross into the path of Ekitike, who glanced the ball home.
As they have done for much of the season, Dortmund dominated possession but were unable to break through, with the hosts holding firm.
With just over 10 minutes remaining, Nnamdi Collins clattered into Jamie Gittens inside the box but the referee waved the contact away before showing Dortmund captain Emre Can yellow for complaining.
Dortmund threw men forwards as Sahin made a series of attacking substitutions, only for Frankfurt's Hojlund to steal the ball from Can and march up the field before sealing the result.
At fulltime, Marmoush emerged from the stands and celebrated with his soon-to-be former teammates for the last time.
On Saturday, league leaders Bayern Munich host Wolfsburg. Defending champions Bayer Leverkusen, who sit four points back in second, play at home against Borussia Moenchengladbach.