There was a lot at stake when Arsenal faced Slavia Prague in the UEFA Europa League quarter-final second leg on Thursday. While other fixtures in the competition had already been decided after the first leg, this one was far from over.Following a 1-1 draw at the Emirates, the two teams had everything to play for and a lot to prove.However, unlike in the first leg, Arsenal rose to the occasion and put in an assured performance away from home.The Gunners were duly rewarded with a heavy 4-0 win, courtesy of goals from Nicolas Pepe and Bukayo Saka as well as a brace from Alexandre Lacazette.Into the semi-final! 🙌 ⚪ 0-4 🔵 (FT) | (1-5 agg) 🏆 #UEL— Arsenal (@Arsenal) April 15, 2021Captain’s performance from Alexandre LacazetteWith Pierre-Emerick Aubameyang ruled out of the game due to malaria, Alexandre Lacazette was named as stand-in captain against Slavia Prague.The Frenchman started the night in iconic fashion. A photo of him taking a knee with the armband strapped to his arm while the Slavia Prague players stood over him unconcerned went viral before kickoff.Once the game itself started, Lacazette was a constant menace in attack and put in a solid performance while leading the line for Arsenal.The 29-year-old's two goals were deserved rewards for his impeccable output against Slavia Prague. This was, by far, one of his best matches in an Arsenal shirt - a true captain’s performance.Unai Emery has reached the Europa League semi-finals more times (6) than any other manager in the competition's history:✖️ 2012 Valencia✓ 2014 Sevilla✓ 2015 Sevilla✓ 2016 Sevilla✓ 2019 Arsenal✓ 2021 VillarrealHe's only been knocked out once. #UEL pic.twitter.com/0IGuC6J1Ez— Squawka Football (@Squawka) April 15, 2021Arsenal set up Unai Emery reunion in Europa League semi-finalsArsenal sealed a 5-1 aggregate win over Slavia Prague, thereby securing a ticket to the semi-finals of the Europa League.A reunion with former boss Unai Emery awaits, with the Spanish manager also guiding Villarreal past Dinamo Zagreb in the other quarter-final fixture.It’s going to be a tough match, but Mikel Arteta must now devise a plan to thwart the tactics of the man whom he replaced at the Emirates.Arteta said after the game (as quoted by Goal):"It will be really tough and Unai Emery is probably the most successful manager in this competition.""There is still a lot to do and things we can improve on, but we have a real desire to improve and be better every day.”Arsenal’s season hasn’t been perfect, but nothing will matter if they win the Europa League. They will be taking a huge step towards that if they manage to overcome Villarreal.