Arsenal have waited three years for a night like this.
With the tie finely poised after last week's 2-2 draw, it promises to be another test of the squad's new mentality, which those inside the club have stressed as being key to their success.
The Gunners have coped with the pressure of being top of the Premier League, and must now show they can handle the heat of a European knockout tie.
It is also the start of a huge four days for the squad. On Sunday, they can go eight points clear of Manchester City at the top of the table with victory over Crystal Palace.
Mikel Arteta is determined to continue fighting on two fronts and is expected to name a strong team for this last-16 clash, with Gabriel Jesus pushing for his first start since November. The Brazilian injured his knee playing at the World Cup, and made his comeback on Sunday for the final 13 minutes of the 3-0 win at Fulham.
Arsenal are aware that he cannot play a full game yet, but Arteta is weighing up starting the striker and giving him an hour.
The manager said: "Gabby is feeling good every day that he's training. He says that these senses are getting better and better, so that's really positive.
"We have to manage his minutes and manage his involvement in the squad and in the team.
"You can feel the happiness of everybody around him: supporters, players, staff. We missed him and now we're glad he's back."
Playing tonight would be a significant step up for Jesus after his cameo during the comfortable win at Fulham.
Given the state of the tie, any tension lacking from Craven Cottage will be present at the Emirates Stadium.
The Gunners reached the Europa League semi-finals in 2021, however that was when fans could not attend games.
Their last European knockout match with supporters was February 2020, when Olympiakos came to Emirates Stadium. Youssef El Arabi scored in the 119th minute to secure a shock 2-1 win for the Greek side and knock the hosts out.
Just three players from the match-day squad that night are still at Arsenal. Hector Bellerin, who started at right-back, is now on loan at Sporting from Barcelona.
"We haven't had big European nights for three years due to Covid especially," said Arteta.
"Obviously, it's been a long time since we had one of those special nights and now we have to build that back."
Arteta will hope tonight is not a repeat of the chaotic first leg. Arsenal lacked control and looked disjointed after the manager made six changes.
He may not make quite as many tonight, but full-backs Kieran Tierney and Takehiro Tomiyasu (left) are both pushing to start.
Sporting boss Ruben Amorim has his own selection headaches, because midfielder Hidemasa Morita and captain Sebastian Coates are suspended.
The loss of Coates is a big blow, as the former Liverpool defender usually plays in the heart of Sporting's back-three. They are braced for a backlash from Arsenal after last week, especially if Jesus plays.
"We gave almost everything that we had in the first leg, but I believe that players can always do better," said Amorim. "If Arsenal speed things up even more, we will have another gear for defending and attacking. We are capable of that."