David Raya proved the hero as Arsenal survived a penalty shootout to scrape past Porto and reach the quarter-finals of the Champions League for the first time in 14 years after a tense last-16 duel had ended 1-1 on aggregate on Tuesday.
Porto, who won the opening leg 1-0, proved stubborn opposition for the Premier League leaders and Arsenal fans must have feared another night of European heartache.
But Martin Odegaard, Kai Havertz, Bukayo Saka and Declan Rice all tucked away their spot kicks with clinical precision and Arsenal keeper Raya made two saves.
He got the slightest of touches to send Wendell's effort against the post and then saved Galeno's penalty to send Arsenal through 4-2 in the shootout and spark wild celebrations.
Leandro Trossard's goal shortly before halftime had levelled the tie but Arsenal struggled to break down a disciplined Porto side who produced a defensive masterclass.
Extra time failed to separate the sides but Mikel Arteta's team held their nerve to snap a run of seven successive exits at the last-16 stage. The last time they reached the quarter-finals in 2010 they also beat Porto in the last 16 and they will go into Friday's draw full of confidence that they can go further.
"For them to do it when the club hasn't done it for 14 years that tells you the difficulty," Arteta, whose side have won eight successive Premier League games to edge ahead of Manchester City and Liverpool, told reporters.
"They are willing to sacrifice anything to win.
It was hard on Porto who produced a classic away performance with 41-year-old defender Pepe a rock at the back and Evanilson twice going close to stunning the hosts.
But they were left deflated as their dreadful record away to English clubs continued with a 20th defeat from 24 games.
ARSENAL FRUSTRATION
Porto's tactic of disrupting Arsenal's attacking rhythm had worked a treat in the first leg when Galeno's stoppage-time goal earned them a 1-0 win and it proved effective again.
Arsenal were restricted to few clear chances in the opening period with Odegaard's shot into the side-netting a rare glimmer of their usual attacking verve.
Backed by a sizeable travelling support, Porto were calm and composed and occasionally threatening with Brazilian striker Evanilson forcing a fine save from Raya.
With halftime approaching anxiety was growing among the home faithful but the mood changed in the 41st minute when Odegaard, so often Arsenal's catalyst, slipped a pass through Porto's defence and Trossard side-footed past Diogo Costa.
The expected Arsenal siege failed to materialise in the second half though as Porto stuck to their script, disrupting the flow of the game with every trick in the book.
Arsenal's frustration boiled over at the midway point of the second half when Pepe tried to shepherd the ball back to his keeper but got in a tangle and Odegaard scored, only for the goal to be harshly ruled out for a foul by Havertz.
Arteta was so incensed at the decision that he received a yellow card and not long after that Porto coach Sergio Conceicao also went into the book as the tension mounted.
With the tie on a knife edge Arsenal's hearts were in their mouths when Francisco Conceicao burst through and forced Raya into another save while at the other end substitute Gabriel Jesus almost scored with his first touch as his close-range shot was saved by the legs of Diogo Costa.
Extra time was a stalemate but Arsenal prevailed in the first Champions League knockout match to go to penalties since the 2016 final between Atletico Madrid and Real Madrid.
"A great moment personally and collectively. I'm over the moon to save two penalties in the Champions League to get through to the quarter-finals," Raya said.