FC Porto snatched a shocking last-gasp 1-0 victory against Arsenal with Galeno netting a sublime effort deep in stoppage time in their Champions League round-of-16 tie Wednesday.

A drab clash was deadlocked until the fifth minute of added time, when Galeno curled an unstoppable effort past David Raya to send the Estadio Do Dragao crowd wild.

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Arsenal, who had scored 21 goals in their past five Premier League games, were strangely subdued in attack and failed to register an effort on target throughout a cagey contest.

It was the first time Arsenal failed to have a shot on goal in a Champions League match since a 3-1 loss to Barcelona in March 2011.

They defended solidly enough but might live to regret their lack of urgency as Galeno gave Porto the edge ahead of the second leg in London on March 12.

Arsenal are seeking to reach the quarterfinals for the first time since 2010, with their past seven Champions League campaigns all having ended in the round of 16.

"We had to manage the game better when you can't win," Arsenal manager Mikel Arteta said. "We lacked threat and aggression in the final third and we need to tweak a few things. We can do better.

"If you want to be in the quarterfinals you have to beat your opponent, and this is what we will have to do at the Emirates now."

Reassuringly for Arsenal, Porto have a terrible record away against English clubs and have never scored at Arsenal, conceding 11 in three visits.

But the 30-time Portuguese champions will travel with hope.

Arteta's side controlled possession throughout the game. But apart from a couple of headers from William Saliba and Kai Havertz, both from corners, never really looked like scoring.

Porto grew in confidence after an incredible incident in the 21st minute when Galeno thumped a shot against the far post and, when the ball came back to him at pace, he placed the rebound agonisingly wide of the other post.

With 40-year-old Pepê, the oldest player to appear in a Champions League knockout round game, showing his vast experience at the back, Porto comfortably dealt with Arsenal's goal threats and England forward Bukayo Saka was very quiet.

Porto occasionally threatened and had another chance shortly before the break when Evanilson drove a shot at Raya.

The second half was even less exciting than the first with Arsenal struggling to gain any rhythm against their wily hosts.

But the best was saved to last as Galeno seized on a loose ball and advanced to the edge of the penalty area before looking up and bending a shot past Raya.

"It was a kick in the teeth," Arsenal midfielder Declan Rice said. "We have to change our approach in the home leg and give it absolutely everything."

Information from Reuters contributed to this report.