With the match tied at one, Ospina made a terrible mistake on a corner kick which put Arsenal behind 2-1 at the break.
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The Colombian goalkeeper was out of position on the corner, and couldn’t get back quickly enough to stop the curling cross. Ospina tried to make a catch and push it out, but he wasn’t able to keep the ball from crossing the line as the assistant referee signaled for a goal.
After falling to Dinamo Zagreb in the first match of group play, a second loss would put a huge damper in Arsenal’s chances of advancing, especially with the Gunners still yet to play Bayern Munich.