Borussia Dortmund missed the chance to put pressure on Bayern Munich after losing 3-1 to Hamburger SV this evening.
Despite dominating possession early on, Dortmund were sloppy for long spells as they struggled to break down a determined Hamburg defence.
The hosts were gifted the chance to break the deadlock when Roman Burki was adjudged to have made contact with Ivo Ilicevic, who had timed his run to perfection to beat the goalkeeper to a through-ball.
Pierre-Michel Lasogga took on the responsibility from 12 yards and slotted home to hand the lead to Hamburg.
In a frustrating first half for Dortmund, their best chance ended with a powerful strike from Marco Reus being tipped past the post by Rene Adler.
Hamburg remained comfortable for long spells before scoring a crucial second when Nicolai Muller found the space to set up Lewis Holtby, who fired home to double the advantage.
It took just 10 second-half minutes for Dortmund to slip further behind in bizarre fashion as Mats Hummels headed into his own net despite being under little pressure while attempting to clear a cross.
The setback came after Thomas Tuchel had introduced Shinji Kagawa and Matthias Ginter at the break, and a disappointing evening continued for the Dortmund boss as he watched Adler spring off his line to keep out Pierre-Emerick Aubameyang's low effort.
Hamburg were happy to drop deeper to protect their advantage, but it was Adler who came to the rescue again to push Ilkay Gundogan's free kick to safety.
A consolation goal arrived for Dortmund late on when Henrikh Mkhitaryan combined with Adnan Januzaj, whose cross was converted by Aubameyang as the visitors unsuccessfully attempted to launch a dramatic fightback.