Benfica's João Félix, 19, was the star of the night, while Arsenal, Chelsea and Valencia made positive starts.
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- João Félix nets three as Benfica beat Eintracht
- At 19, youngest to hit Europa League hat-trick
- Arsenal make positive start at home v Napoli
- Valencia and Chelsea both win on the road
- Highlights from midnight wherever you are
Quarter-final first legs
Arsenal 2-0 Napoli
It is advantage Arsenal after a scintillating first-half performance. The hosts were 2-0 up inside 25 minutes, Aaron Ramsey rounding off a delectable team move before Lucas Torreira's shot was deflected in off Kalidou Koulibaly. Both teams had chances in an open second period but the damage was done.
Villarreal 1-3 Valencia
Gonçalo Guedes converted the rebound after an early penalty was saved but it was level by the break, Santi Cazorla registering from the spot. Villarreal buckled at the last though, Daniel Wass making it 2-1 to the visitors in added time before Gonçalo Guedes broke away to give Valencia a two-goal lead.
Benfica 4-2 Eintracht Frankfurt
At 19, João Félix became the youngest player to score a UEFA Europa League hat-trick. His first came from the spot after Evan N'Dicka was sent off for a foul, and he restored Benfica's lead after Luka Jović replied. João Félix teed up Rúben Dias for Benfica's third before completing his treble. Gonçalo Paciência's header gave Eintracht hope.
Slavia Praha 0-1 Chelsea
Marcos Alonso headed in Willian's 86th-minute cross to give the 2013 winners the advantage heading back to London. Willian had hit a post and Antonio Rüdiger was denied by Ondřej Kolář but the visitors were grateful to Kepa Arrizabalaga, who saved well from Ibrahim-Benjamin Traoré and Jan Bořil at 0-0.
Quarter-final second legs: Thursday 18 April
Semi-final first legs: Thursday 2 May
Arsenal/Napoli v Villarreal/Valencia
Benfica/Eintracht Frankfurt v Slavia Praha/Chelsea
Semi-final second legs: Thursday 9 May
Villarreal/Valencia v Arsenal/Napoli
Slavia Praha/Chelsea v Benfica/Eintracht Frankfurt
Final: Olympic Stadium, Baku, Wednesday 29 May
Benfica/Eintracht Frankfurt/Slavia Praha/Chelsea v Villarreal/Valencia/Arsenal/Napoli
All kick-offs 21CET