Inter scored the first goal conceded by Arsenal in the Champions League so far this season, as Hakan Calhanoglu converted a penalty following Mikel Merino's handling offence.
See how that game unfolds on the Liveblog.
The midfielder was making his return to the starting XI after a month out with a muscular issue and his free kick into the box was kicked onto the arm of Merino by Mehdi Taremi.
Romanian referee Istvan Kovacs immediately pointed to the spot to award the penalty for handball.
Although it could be argued that the ball was kicked onto his arm from point-blank range, Merino also had his hand in an unnatural position for defending in that situation.
Calhanoglu has a simply extraordinary record on penalties, converting all 19 of them in the Inter jersey.
In his entire career, he failed to convert only five out of 48 between club and international competition.