Arsenal manager Arsene Wenger says his side have done "half a job" after a "spectacular" first-half performance saw the Gunners take control of their Europa League quarter-final by demolishing CSKA Moscow in the first leg.
Alexandre Lacazette and Aaron Ramsey scored two goals each as the Gunners hit four in 26 minutes before half-time.
Arsenal were unable to add to their tally in the second half but they will head to Russia's capital for the second leg next Thursday with a commanding lead.
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"We have to be realistic. We have to do the job over there, go and try to win the game, that's the best way," said Wenger.
Ramsey's side-foot finish set Arsenal on their way.
Aleksandr Golovin levelled with a sublime free-kick before France striker Lacazette, who has recovered from a knee injury, made it 2-1 with a penalty after Mesut Ozil was fouled by Georgi Schennikov.
Ramsey produced a brilliant third with an instinctive volleyed flick, with Lacazette adding a fourth after being picked out by the outstanding Ozil.
"We have done half of a job," added Wenger. "There was a good pace in the first half, the two teams gave everything, which is why is was such a spectacular first half."
Koke's goal after 23 seconds set Europa League favourites Atletico Madrid on their way to a quarter-final first-leg on over Sporting Lisbon.
Ex-Chelsea striker Diego Costa took advantage of a defensive mistake seconds into the game to set Koke up.
And Antoine Griezmann added a second after taking advantage of another Sporting error.
Costa missed two chances to add a third in the second half, following more calamity at the back.
Atletico, the 2010 and 2012 Europa League winners, have now won their past nine matches at the Wanda Metropolitano.
Lazio took a big step towards the semi-finals with a dramatic 4-2 win over Red Bull Salzburg, whose 19-game unbeaten run in Europe - and 36-match streak without losing in all competitions - came to an end.
The hosts led after eight minutes through captain Senad Lulic, but Valon Berisha equalised with a penalty.
Marco Parolo backheeled the Serie A side back into the lead before Takumi Minamino levelled seconds after coming off the bench.
But Felipe Anderson and Ciro Immobile, who has now scored 37 goals this season, put Lazio in control of the tie.
Timo Werner scored the only goal as RB Leipzig beat Marseille 1-0 in a close first leg.