Borussia Dortmund blew the Champions League's group of death wide open as Felix Nmecha's goal beat Newcastle 1-0 at St James' Park on Wednesday.
Newcastle twice hit the woodwork in the closing stages through Callum Wilson and Fabian Schar, but now have work to do to reach the last 16 on their return to the competition after 20 years.
The German giants' first win in Group F lifts Dortmund above Newcastle on head-to-head record with both sides on four points.
Paris Saint-Germain lead the section on six points with last season's semi-finalists AC Milan bottom on two.
Newcastle had announced their return to the Champions League stage in style with a 4-1 demolition of PSG three weeks ago.
But the Magpies were handed a deserved reality check after a surprisingly flat performance.
Dortmund had failed to score in their opening two games in the toughest group in the draw.
But their defeat by PSG last month was the only time they have lost in 12 games so far this season.
Dortmund dominated the opening 45 minutes, but should still have fallen behind when Anthony Gordon fired straight at Gregor Kobel with just the Swiss goalkeeper to beat.
Newcastle were then dealt a major blow when former Dortmund striker Alexander Isak was forced off with injury.
Donyell Malen and Niclas Fullkrug tested Nick Pope but it was an inspired piece of play from a centre-back that eventually helped Edin Terzic's men break their duck.
Nico Schlotterbeck robbed Gordon of possession in midfield and burst forward before crossing for Nmecha to stroke into the far corner in first-half stoppage time.
Sandro Tonali is expected to be handed a 10-month ban in the coming days for alleged breaches of betting rules during his time with AC Milan.
However, Eddie Howe still turned to the Italian international off the bench to try and inspire a turnaround.
Newcastle were left to rue one huge missed opportunity when Isak's replacement, Wilson, fired into Kobel's legs with just the goalkeeper to beat.
Wilson then saw a flicked header come back off the crossbar.
Howe's men came even closer in the dying seconds of stoppage time as Schar's deflected effort looped over a helpless Kobel and bounced kindly back off the bar for Dortmund into the path of a covering defender.
But the visitors clung on to leave the group delicately poised heading into another clash between the sides in Dortmund on November 7.
kca/jc
