Paris: Arsenal and Chelsea closed in on the Europa League last four on Thursday after the Gunners saw off highly-fancied Napoli 2-0 at the Emirates, while Marco Alonso's late header earned Maurizio Sarri's side a hard-fought win at Slavia Prague.
Unai Emery's Arsenal hold a healthy advantage going into next week's second leg thanks to a fine early strike from Juventus-bound Aaron Ramsey and an unfortunate Kalidou Koulibaly own goal midway through the first half, and can rue missed chances that would have put the tie completely beyond the Italians' reach.
Chelsea meanwhile escaped from Eden Arena after a bitty display that saw Kepa Arrizabalaga have to make some fine saves to keep the Czechs out before Alonso nodded home Willian's pinpoint cross four minutes from time to seal a 1-0 win.
The Premier League pair remain on a collision course for the final in Baku, with both sides set to avoid each other if they make it through next week's second legs.
Arsenal were all over Napoli from the kick-off and got their deserved opener with 14 minutes on the clock, Ramsay waltzing in at the end of a beautiful passing move to calmly stroke home Ainsley Maitland-Niles's neat lay-off.
Napoli were completely out of sorts, barely able to get the ball out of their own half at times, and 10 minutes later the Gunners doubled their lead.
Former Sampdoria midfielder Lucas Torreira won possession in midfield and charged towards goal before letting off a weak shot that flicked off Koulibaly and flew past a bamboozled Alex Meret in the Napoli goal.
Arsenal should have made more of their first-half dominance over Carlo Ancelotti's slipshod side, but were not punished by the Serie A outfit, who through Piotr Zielinski should have bagged an away goal to take back to Naples in the second half.
Felix on fire
Arsenal will almost certainly take on Valencia should they hold on at what will be an intimidating Stadio San Paolo after the La Liga side scored twice in stoppage time to win 3-1 at fellow Spaniards Villarreal.
Goncalo Guedes scored twice, including what could be the decisive third three minutes into added time, as Marcelino's side struck with two clinical breakaway goals to give them a great chance of making the semis.
Chelsea meanwhile will likely play Benfica should they go through, after young gun Joao Felix fired them to a 4-2 win over Eintracht Frankfurt with a hat-trick that leaves the Bundesliga side, who had to play with 10 men for 70 minutes, with an uphill task to make the last four in Germany next week.
Felix got the ball rolling for Benfica, who are also neck-and-neck with Porto in the Primeira Liga title race, from the spot in the 21st minute after Evan N'Dicka was sent off for shoving over goal-bound Gedson Fernandes.
He put the hosts back in front just before the break after Luka Jovic -- on loan from Benfica -- scored a shock leveller against his parent club in the 40th minute.
Ruben Dias made it three when he headed in Felix's flick-on a from a corner, and the 19-year-old side-footed home Alex Grimaldo's cross to complete his treble nine minutes into the second half, before Goncalo Paciencia pulled one back with his head from a corner to keep the tie alive.