When the Champions League anthem reverberated inside the Emirates Stadium, there was a genuine sense of occasion. It had been seven years since the Gunners had played at this level of European football's top competition, and fourteen years since it had advanced to the quarterfinals.
Porto came into the match defending a 1-0 lead from the first leg, but Martin Odegaard's deft reverse pass set up Leandro Trossard for an inch-perfect strike that leveled the score for Arsenal in the first half.
The game ended 1-0 after extra time on the night despite pressure from Arsenal and opportunities for both teams to score the winning goal.
The men from Arsenal eventually showed resilience to score all four of their penalties, as the excellent David Raya stopped the spot kicks from Brazilians Wendell and Galeno.
Mikel Arteta, the manager of Arsenal, declared that this was arguably the best atmosphere he had seen at the Emirates Stadium since taking over in 2019. It was a boisterous evening.
Regarding the home crowd, he added, "They were amazing," calling the evening "magical."
Well over an hour before kickoff, the 3,000 Porto supporters who had traveled from abroad filled the stadium's renowned Clock End corner, serenading their goalkeepers as they came out of the tunnel for the pre-game warm-ups.
Thirty minutes later, the rest of the team emerged to an even louder reception, with the evergreen 41-year-old captain Pepe leading the raucous cheers from the away fans.
For the team's first home knockout match in the Champions League since 2017, Arsenal manager Mikel Arteta had urged Gunners supporters to "bring the noise." As the teams were ready to kick off, they dutifully complied, filling the north London sky with a booming rendition of the club's anthem, "North London Forever."
Instead of merely being pleased to be back in Europe's top competition, supporters of Arsenal actually believe that this side can create some genuine noise this season. However, Tuesday's match will serve as a sobering reminder of exactly how cruel the Champions League can be.
Arsenal dominated the first few minutes, as was to be expected, although Porto striker Evanilson had a chance to score from outside the box, but he missed it due to a bad header from defender William Saliba.
It served as a reminder of the threat this Porto club posed, should Arsenal still require one following Galeno's late, long-range steal in the first leg.
However, it appears that Arsenal disregarded the warning since, a few moments later, the defense gave Evanilson enough time in the penalty area to control a ball and attempt a goal; Raya's wise stop kept the score tied.
Porto was progressively rising to the occasion despite Arsenal's early domination, but with five minutes left in the half, the away team's solid effort from the first forty minutes was undone.
Trossard was in space inside the area when Odegaard's exquisite pass found him, and the Belgian striker expertly placed the ball into the bottom corner of the net.
Long before kickoff, the Emirates had been building up to this moment, and they finally let go.
Arsenal's second-half progress was spurred on by the goal, as Porto appeared to be prepared to stand back and take the pressure.
When Pepe appeared to get tangled up defending a long ball, Odegaard was able to chip the ball into the open net, giving the home team the appearance of taking the lead in the match for the first time.
But after it was determined that Kai Havertz had tugged Pepe's jersey, the goal was not permitted.
Flitting around his technical area and shouting directions, Arteta appeared to be covering as much distance as his players. Outraged by the decision, Arteta protested and was given a yellow card.
Following the game, Arteta told reporters, "Live, I couldn't understand but the referee made the decision, maybe there was something there."
"We'll remember that we did it in our own unique way, and I'm sure we won't remember that."
Even though defense was now Porto's top concern, the squad occasionally looked threatening going forward, as Francisco Conceição tested Raya with a low shot following a quick counterattack.
Arsenal persisted in their pressure and had opportunities to win the match through Bukayo Saka and Odegaard, but it was becoming more and more likely that extra time would be needed.
Extra time was mostly uneventful after an exciting ninety minutes, with Havertz's push on Porto manager Sergio Conceição starting a fight on the touchline.
The home advantage that Arsenal had later proved crucial in the penalty shootout. Wendell and Galeno lost concentration in the face of a wall of noise and whirling red and white scarves, and their failed penalties proved costly for Porto as Arsenal supporters serenaded their manager with a last performance of "Super Mik Arteta."