Galeno curled in a sublime stoppage-time strike as FC Porto defeated Arsenal 1-0 in the first leg of their Champions League last-16 tie in Portugal on Wednesday, while a dominant Barcelona were held 1-1 at Napoli.

Appearing in a first knockout match in Europe's premier club competition for seven years, Arsenal struggled to break down an organised Porto defence before Galeno's last-gasp stroke of brilliance.

Porto, European champions in 1987 and 2004, are a disappointing third in Portugal this term, but frustrated Arsenal throughout.

They were happy to cede possession and allow Arsenal to dictate the tempo in the first half, but it was the hosts who created the best chance.

Francisco Conceicao darted in from the right and slid over a cross that looped off a sliding Gabriel, with Galeno rifling against the far post and then steering the rebound wide after the ball came right back to him.

William Saliba and Kai Havertz headed wide at corners either side of a Nico Gonzalez drive that sailed over in a physical opening 45 minutes.

Leandro Trossard, deployed again as the leader of the attack alongside Bukayo Saka and Gabriel Martinelli, lashed over on the volley from Declan Rice's driven corner early in the second half.

Arteta made his first change with a quarter of an hour left, replacing Trossard with Jorginho, as Arsenal sought additional control in the closing minutes only to be undone by a moment of magic from Galeno.

Barcelona were the better team for large parts of the game in Naples but return to Spain level after Victor Osimhen snatched a draw with the hosts' only shot on target.

Xavi's team, who scored through Robert Lewandowski, created more chances and were agonisingly close to getting a last-gasp win when Ilkay Gundogan's low shot whizzed just wide.

"It's a shame that the result didn't reflect the play. But I'm satisfied because we applied what we have worked on. I'm proud of the image the squad gave of itself. We're ready to compete in the return leg," Xavi told reporters.

New Napoli boss Francesco Calzona was also happy with the result of his first match, which was prepared hurriedly after becoming the Italian champions' third manager of the season on Monday night.

"What I liked best was the desire to get back into the game. We need to work on tactical things, but I also got good responses from the substitutes so I'm happy," said Calzona. (AFP)