UEFA Champions League: Arsenal's return to the knockout stages of the UEFA Champions League did not go to plan after a strike from Galeno in the fourth minute of second-half stoppage time gave Porto a 1-0 win in the first leg of their last-16 tie.
Galeno scored a brilliant goal on Wednesday night to give the Portuguese team the advantage ahead of the second leg at Emirates Stadium.
Arsenal struggled to create chances like they have in recent matches as they failed to register a shot on target for the first time this season.
The first real clear-cut chance of the night fell to the hosts, with Galeno thundering a shot onto the post and then putting the rebound narrowly wide with 21 minutes gone.
Arsenal's potent front line was kept quiet by some disciplined Porto defending, and the Gunners failed to carve out an opening until centre-back William Saliba headed wide from Bukayo Saka's corner in the 35th minute.
The second half continued in a similar vein, with Porto frustrating the Arsenal attack despite the Gunners pressing higher up the pitch. Their clearest sight of goal came when defender Gabriel headed a Declan Rice free-kick over the bar as full time approached.
That was swiftly followed by the evening's most dramatic moment, however, as Galeno made amends for his earlier miss by bending in a superb long-range, right-footed effort to send the home fans wild.
In the end, Arsenal were unable to muster a single shot on target during the entire match. The result leaves the tie beautifully poised for what should be a fascinating second leg in London in just under three weeks' time.
"I think the credit for that goal goes to the whole team, for what they did in the 90 minutes. We played well, we defended well, we left all our energy on the pitch. Regarding the goal, when the opportunity arose, I didn't hesitate. I am very happy. We will try to replicate in London what we achieved here. We will try to stay solid and give our best, as we always do," Galeno said after the match.