This was a German attack which drove off the Romanian forces from the Transylvanian coal mining center of Petrozsény (the present-day city of Petroșani in Hunedoara County, Romania).

[1]: 21–22 [2]: 293 [3] Given that this was a region of valuable coal mines which were vital for the Hungarian railways, this was the area where the first Central Powers counterattack against the Romanian offensive in Transylvania was launched.

Despite German support, the Austro-Hungarian commander of the 144th Infantry Brigade, Colonel Ludwig Berger, "inexplicably" ordered a retreat.

[5] By 12 September, three-fourths of the distance between the Transylvanian border and the vital junction of Hátszeg (Hațeg) had been covered by the Romanian Army.

[3] German General Hermann von Staabs, the commander of the XXXIX Corps which had assumed responsibility on 8 September for operations in the southern region of Transylvania, reacted quickly to the Austrian withdrawal.

On the 9th, Major Radu R. Rosetti from the Romanian headquarters stated to General Andrei Zayonchkovski – the Russian commander of the Dobruja Army – that the 2nd and 12th Divisions "were coming from Transylvania".

[9] On 18 September, after heavy fighting, the large German force commanded by General von Staabs pushed the Romanian troops back and entered Petrozsény.

[1]: 99 [7] The inexperienced Romanian 11th Division commander, Brigadier General Ioan Muică, retreated to Bumbești, allowing Sunkel's troops to take the Szurdok (Surduc) Pass on the following day.

[1]: 99–100  In his memoirs, Erich Ludendorff stated that, on 19 September, the German troops were successful in throwing back the Romanian units near Petrozsény over the mountain ridge.

[14][15] The three divisions of the 9th Army concentrating at Szászsebes (Sebeș/Mühlbach) could be enveloped by the Romanian forces from the region of the two mountain passes, and – according to German planning – this was the possibility to be dealt with first.