AC Milan, Arsenal, Atlético and Marseille made comfortable starts in their round of 32 ties, but the second legs look set to provide serious headaches for Dortmund, Napoli and Zenit.
AC Milan, Arsenal Atlético Madrid and Marseille will feel they have one foot in the round of 16 after kicking off their ties with wins by three-goal margins, and things are looking pretty healthy for Athletic Club too after 37-year-old Aritz Aduriz struck twice in a 3-1 success at Spartak Moskva.
Dortmund have more work to do after striking late to earn a 3-2 win against Atalanta in Germany while Napoli are in trouble following a 3-1 home loss to Leipzig.
Final hosts Lyon have the edge in their tie following a 3-1 home success against Villarreal.
Östersund 0-3 Arsenal
Dortmund 3-2 Atalanta
Ludogorets 0-3 AC Milan
Napoli 1-3 Leipzig
København 1-4 Atlético Madrid
Marseille 3-0 Braga
Real Sociedad 2-2 Salzburg
Nice 2-3 Lokomotiv Moskva
Spartak Moskva 1-3 Athletic Club
Celtic 1-0 Zenit
Lyon 3-1 Villarreal
Partizan 1-1 Viktoria Plzeň
FCSB 1-0 Lazio
AEK Athens 1-1 Dynamo Kyiv
Astana 1-3 Sporting CP
Crvena zvezda 0-0 CSKA Moskva (Tuesday)
The second legs are next Thursday with the exception of CSKA Moskva v Crvena zvezda, which takes place on Wednesday to avoid a clash with Lokomotiv Moskva v Nice. The round of 16 draw is next Friday at 1pm.