AC Milan withstood a late onslaught to beat Celtic 3-1 and AZ Alkmaar overcame the loss of 13 players with positive Covid-19 tests to secure a shock 1-0 win at Napoli.
Arsenal came from behind to down Rapid Vienna 2-1 and Spurs Spurs beat LASK 3-0 in the opening round of Europa League group stage matches.
Arsenal, the 2019 finalists under Unai Emery, were struggling to make an impact in Austria on Thursday.
After a goalless first half they went behind when keeper Bernd Leno fluffed a clearance on a night he will want to forget.
Taxiarchis Fountas capitalised on Leno's clanger, much to the joy of the 3,000 home fans allowed in to watch under coronavirus safety protocol, but the Gunners then turned the game around in four second half minutes.
David Luiz put them level with a deft glancing header off Nicolas Pepe's free-kick, with Pierre-Emerick Aubameyang then tapping home to bag the three Group B points.
It was an eventful night for Mikel Arteta's side with alongside eight yellow cards an eye catching display from Thomas Partey on his first start since his transfer deadline day move from Atletico Madrid.
A frustrated follower of the game from his London sofa was Mesut Ozil, who has been left out of both Arsenal's Europa League and Premier League squad.
"When I can't support on the pitch tonight, I will support in front of the TV in London." tweeted Ozil.
The other Group B game was being played out in Dublin where Dundalk, only Ireland's third ever representative in the group stage, were beaten 2-1 by Norwegians Molde.
Dutch team Alkmaar were under pressure for the whole game as Napoli dominated possession and peppered their goal but Dani de Wit scored in the 57th minute for a stunning victory in Group F.
With Milan’s defence well marshalled by Danish centre-back Simon Kjaer, they looked to be cruising to an easy win at Celtic after first-half goals from Rade Krunic and Brahim Diaz.
However, the Scottish champions came roaring back in the second half and reduced the deficit through Mohamed Elyounoussi. Milan needed a late goal from Jens Petter Hauge, his first for the club, to put the Group H game out of reach.
Celtic’s disappointment was summed up by midfielder Ryan Christie. “I’m gutted to lose tonight, I did feel like we could have pushed forward and got an equaliser, but there’s positives to take from the second half,” he said.
Villarreal and Turkey’s Sivasspor played out an eight-goal thriller in Group I, with the Spanish side grabbing a 5-3 win thanks to a late double from striker Paco Alcacer
In Belgium, Steven Gerrard's Rangers took on Standard Liege fresh from their Old Firm derby win over Celtic which moved them four points clear in the Scottish Premiership last weekend.
With the rain coming down, James Tavernier scored from the spot after Noe Dussenne handled in the area to put them into a 19th minute lead.
Then three minutes into stoppage time Kemar Roofe produced a wonder goal from the halfway line, the ball flying over the head of bewildered keeper Arnaud Bodart.
Benfica had claimed the first goal of the night and they went on to beat Lech Poznan in Poland 4-2 in the other Group D game.
Elsewhere, Bayer Leverkusen ran riot 6-2 against French side Nice and Spanish side Granada, in their first ever European campaign, beat PSV Eindhoven 2-1.
Later, Tottenham host Austrian side LASK with Gareth Bale making his first start since returning to Spurs on a season-long loan.
Seven-time European Cup winners AC Milan are at Celtic, and Leicester host Zorya Luhansk of Ukraine.
Can Spanish sides be stopped?
Sevilla's triumph over Inter Milan in last season's final means Spanish teams have won the Europa League in seven of the past 11 years. Sevilla have won four of those, while Atletico Madrid have won three.
The trophy has been won by Spanish sides 10 times since 2004.
Real Sociedad and Villarreal look capable of doing well, while Granada will also hope to make an impression in their debut European campaign.
READ MORE: Bayern beat Sevilla to win UEFA Super Cup
UEFA Europa League scores:
CSKA Sofia (BUL) 0 CFR Cluj (ROM) 2 (Rondon 53, Deac 74-pen)
Young Boys (SUI) 1 (Nsame 14-pen) Roma (ITA) 2 (Peres 69, Kumbulla 74)
Dundalk (IRL) 1 (Murray 35) Molde (NOR) 2 (Hussain 62, Omoijuanfo 72-pen)
Rapid Vienna (AUT) 1 (Fountas 51) Arsenal (ENG) 2 (Luiz 70, Aubameyang 74)
Bayer Leverkusen (GER) 6 (Amiri 11, Alario 16, Diaby 61, Bellarabi 79, 83, Wirtz 87) Nice (FRA) 2 (Gouiri 31, Claude-Maurice 90)
Hapoel Beer-Sheva (ISR) 3 (Agudelo 45, Acolatse 86, 88) Slavia Prague (CZE) 1 (Provod 75)
Standard Liege (BEL) 0 Rangers (SCO) 2 (Tavernier 19-pen, Roofe 90+3)
Lech Poznan (POL) 2 (Ishak 15, 48) Benfica (POR) 4 (Pizzi 9-pen, Nunez 42, 60, 90+3)
PSV Eindhoven (NED) 1 (Goetze 45+1) Granada (ESP) 2 (Molina 57, Machis 66)
PAOK (GRE) 1 (Murg 56) Omonia Nicosia (CYP) 1 (Bautheac)
Napoli (ITA) 0 AZ Alkmaar (NED) 1 (De Wit 57)
Rijeka (CRO) 0 Real Sociedad (ESP) 1 (Bautista 90+3)
Sporting Braga (POR) 3 (Galeno 44, Dias Fernandes 78, Horta 88) AEK Athens (GRE) 0
Leicester City (ENG) 3 (Maddison 29, Barnes 45, Iheanacho 67) Zorya Luhansk (UKR) 0
Sparta Prague (CZE) 1 (Dockal 47) Lille (FRA) 4 (Yusuf 45+1, 60, 74, Ikone 66)
Celtic (SCO) 1 (Elyounoussi 76) AC Milan (ITA) 3 (Krunic 14, Diaz 42, Hauge 90+2)
Maccabi Tel-Aviv (ISR) 1 (Cohen 10) Qarabag (AZE) 0
Villarreal (ESP) 5 (Kubo 13, Bacca 20, Foyth 57, Paco Alcacer 74, 78) Sivasspor (TUR) 3 (Kayode 33, Yatabaré 43, Gradel 64)
Tottenham Hotspur (ENG) 3 (Lucas 18, Andrade Cedeno 27-og, Son Heung-min 84) LASK (AUT) 0
Ludogorets (BUL) 1 (Marín Escavy 46) Antwerp (BEL) 2 (Gerkens 63, Rafaelov 70)
Wolfsberg (AUT) 1 (Liendl 42-pen) CSKA Moscow (RUS) 1 (Gaich 5)
Dinamo Zagreb (CRO) 0 Feyenoord (NED) 0
Slovan Liberec (CZE) 1 (Helal 30) Ghent (BEL) 0
Hoffenheim (GER) 2 (Baumgartner 64, Dabour 90+3) Red Star Belgrade (SRB) 0