Celtic threw away a two-goal lead to lose 4-3 to Betis and West Ham were 2-0 winners away to Dinamo Zagreb
Victor Osimhen scored twice as Napoli came from 2-0 down to salvage a 2-2 draw at Leicester City, while Lyon cruised to a 2-0 win at Rangers on the opening night of the Europa League group stages.
Earlier, Celtic threw away a two-goal lead to lose 4-3 to Real Betis and West Ham United were convincing 2-0 winners away to Dinamo Zagreb.
Leicester just missed out on Champions League football for a second consecutive season as they finished fifth in the Premier League last term.
But the Foxes are keen to go further than their run to the last 32 of the Europa League last season and got off to a great start against the Italian giants.
Ayoze Perez fired home at the back post from Harvey Barnes' cross after just nine minutes.
Patson Daka then saw his first Leicester goal ruled out by a Video Assistant Referee review for a marginal offside call, but Barnes quickly put that disappointment behind Brendan Rodgers' men with an excellent finish to double Leicester's lead.
Napoli boss Luciano Spalletti held nothing in reserve with his strongest side and the visitors responded in the final quarter thanks to Osimhen.
The Nigerian, who cost €70m ($83m) from Lille last year, brilliantly flicked the ball over the imposing presence of Jannik Vestegaard and Kasper Schmeichel to get Napoli back in the game.
Osimhen then outjumped Caglar Soyuncu to power home a head for a deserved equalizer.
And Leicester's night got even worse in stoppage time when Wilfred Ndidi was sent off in stoppage time for a second bookable offence.
At Ibrox, Lyon spoiled Steven Gerrard's 50th European game in charge of Rangers.
Toko Ekambi curled home from long range to open the scoring midway through the first-half and a goalmouth scramble early in the second period ended with the ball ricocheting off Rangers captain James Tavernier into his own net.
Rangers were outclassed by the French side.
Celtic returned to Seville 18 years on from reaching the Uefa Cup final and got off to a dream start at Benito Villamarin.
Albian Ajeti bundled home the opener thanks to a VAR review after the goal had initially been ruled out for handball before Josip Juranovic buried his first Celtic goal from the penalty spot.
But two goals in three minutes wiped out Celtic's lead as Juan Miranda slotted home before Borja Iglesias unselfishly teed up Juanmi to equalize.
Iglesias completed the comeback with a near post flick early in the second-half before Juanmi's shot flew in off the inside of the box.
Anthony Ralston pulled a goal back three minutes from time to give Celtic some hope, but Betis held on for all three points.
Bayer Leverkusen were also winners in Group G as the Germans came from behind to beat Ferencvaros 2-1 thanks to a second-half winner from 18-year old star Florian Wirtz.
West Ham enjoyed a far more comfortable return to European football in the Croatian capital that had manager David Moyes dreaming of how far they can go.
Michail Antonio pounced off a slack back pass to continue his early season scoring streak with his fifth goal in as many games.
Declan Rice then galloped from inside his own half before producing a powerful finish five minutes into the second-half.
Rangers 0 Lyon 2 (Ekambi 23, Slimani 55)
Brondby 0 Sparta 0
Eindhoven 2 (Goetze 32, Gakpo 54) Sociedad 2 (Januzaj 34, Isak 39)
Monaco 1 (Diatta 66) Sturm Graz 0
Leicester 2 (Perez 9, Barnes 64) Napoli 2 (Osimhen 69, 87)
Olympiakos 2 (El-Arabi 52, Reabciuk 87) Antwerp 1 (Samatta 75)
Frankfurt 1 (Lammers 41) Fenerbahce 1 (Ozil 10)
Galatasaray 1 (Strakosha 67-og) Lazio 0
Lokomotiv 1 (Anjorin 89) Marseille 1 (Under 59-P)
Midtjylland 1 (Isaksen 3) Ludogorets 1 (Despodov 32)
Red Star 2 (Rodic 75, Katai 85-P) Braga 1 (Galeno 76)
Leverkusen 2 (Palacios 37, Wirtz 69) Ferencvaros 1 (Mmaee 8)
Betis 4 (Miranda 32, Juanmi 35, 53, Iglesias 51) Celtic 3 (Ajeti 15, Juranovic 27-P, Ralston 87)
Zagreb 0 West Ham 2 (Antonio 22, Rice 50)
Vienna 0 Genk 1 (Onuachu 90+2)