Borussia Dortmund trail Mainz 05 1-0 at the break of their Bundesliga clash after conceding a first-minute goal.
Elkin Soto's lightning-quick strike at the Westfalenstadion has left Jurgen Klopp's strugglers facing another uncomfortable second half in front of their own fans.
Dortmund beat Freiburg 3-0 last weekend to move out of the relegation zone with a first win in six games, but went behind immediately as Roman Weidenfeller's scuffed clearance was collected by Soto, who smartly lobbed the keeper from 25 yards.
The hosts nearly levelled four minutes into a dramatic opening to the contest as sought-after playmaker Marco Reus, who signed a new contract this week, rattled the post from the edge of the box.
More equalising chances came and went as Mainz keeper Stefanos Kapino produced a crucial save to deny Pierre-Emerick Aubameyang, after the striker had been released by Shinji Kagawa's inch-perfect pass.
In the final stages of the half, Kapino's poor punch saw Kagawa himself come close with a half-volley that whistled past the post, while Reus fired over from 12 yards after being picked out by a Lukasz Piszczek cross.
