Atletico Madrid's Antoine Griezmann celebrates after scoring against Copenhagen. (AFP)
London - Italian league leaders Napoli went ahead against Leipzig but slumped to a 3-1 defeat after a Timo Werner brace
Napoli went down 3-1 at home to RB Leipzig, Arsenal, Atletico Madrid and AC Milan enjoyed comfortable away wins, and Borussia Dortmund's Michy Batshuayi scored twice to secure a 3-2 victory in Europa League last 32, first leg action on Thursday.
Italian league leaders Napoli went ahead against Leipzig but slumped to a 3-1 defeat after a Timo Werner brace, Arsenal overcame Sweden's Ostersunds 3-0 helped by an own goal and Milan won by the same score against Bulgarian champions Ludogorets.
Batshuayi took his tally to five goals in three games since joining Dortmund on loan from Chelsea, with his double against Atalanta hauling the Germans side back from 2-1 down after Josip Ilicic scored twice for the Italians.
Nice striker Mario Balotelli also scored two goals against Lokomotiv Moscow only to be upstaged by a Manuel Fernandes hat-trick as the visitors hit back to win 3-2.
Twice former winners Atletico Madrid recovered from an early fright to win 4-1 at FC Copenhagen as Saul Niguez, Kevin Gameiro, Antoine Griezmann and Vitolo shared the goals after Victor Fischer had put the Danish side in front. FCSB, formerly Steaua Bucharest, beat Lazio 1-0 and Celtic beat Zenit by the same score.
Napoli coach Maurizio Sarri has made it clear that his priority lies in Serie A and a disappointingly sparse crowd turned up for the visit of Leipzig. Adam Ounas gave Napoli the lead early in the second half, the Algerian's first goal for the club, but the away side made the most of shoddy defending to turn the game around.
Werner levelled with an opportunist finish, then Bruma finished off a counter-attack and Werner added another in stoppage time as Napoli were again caught on the break. Arsenal's Nacho Monreal and Mesut Ozil were on target at Ostersunds either side of a Sotirios Papagiannopoulos own goal.
Like the Londoners, Milan's best hope of Champions League football next season appears to be by winning the Europa League.
Patrick Cutrone, a Ricardo Rodriguez penalty and Fabio Borini gave them an impressive win at Bulgarian champions Ludogorets. Balotelli took his tally to 21 goals this term for Nice, where he is in his second season enjoying a new lease of life.
The maverick Italian slotted home after four minutes and converted a penalty in the 28th, sending Lokomotiv keeper Guilherme the wrong way after a Nemanja Pejcinovic handball.
Not to be outdone, Fernandes replied with a penalty and curled in a free kick to equalise in the 67th before completing his second hat-trick this term from Anton Miranchuk's cross.
Athletic Bilbao striker Aritz Aduriz, 37, scored twice in a 3-1 win at Spartak Moscow, while their Basque rivals Real Socieded were held 2-2 at home by Salzburg.
Sporting's Bruno Fernandes, Gelson Martins and Seydou Doumbia scored in an eight-minute spell after halftime as they came from behind to win 3-1 on Astana's artificial pitch in Kazakhstan where Marin Tomasov gave the hosts an early lead.
The roof was closed for the match with temperatures hovering around minus 20 Celsius outside.