Arsenal, Real Madrid, Tottenham, Qarabağ and debutants Union Saint-Gilloise made victorious starts to their league phase campaigns on Tuesday, while Juventus and Borussia Dortmund settled for a point apiece after a pulsating encounter.
UEFA.com rounds up all the action.
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Tuesday night's action
Athletic Club 0-2 Arsenal
Highlights: Athletic Club 0-2 Arsenal
Substitutes Gabriel Martinelli and Leandro Trossard struck to give Arsenal a winning start in a tight contest in Bilbao, with Athletic Club making their first Champions League appearance since 2014/15.
Neither goalkeeper was unduly troubled until Martinelli scored within seconds of his introduction, collecting a Trossard flick from inside the visitors' half and charging through to slot in. Another blistering Martinelli run created the second goal, teeing up Trossard to seal victory with a deflected finish.
Player of the Match: Gabriel Martinelli (Arsenal)
Matchday 2
01/10: Borussia Dortmund vs Athletic Club
01/10: Arsenal vs Olympiacos
All kick-off times 21:00 CET unless stated
PSV Eindhoven 1-3 Union Saint-Gilloise
Highlights: PSV 1-3 Union SG
Union SG made it a memorable Champions League debut with a convincing victory against 1988 winners PSV. Promise David converted a cool ninth-minute penalty and the visitors doubled their lead in style just before half-time when Anouar Ait El Hadj completed a surging solo run with a neat finish.
Kevin Mac Allister dashed any hopes of a PSV comeback when bundling in from close range in the 81st minute, though Ruben van Bommel gave the home side the last word with added time approaching.
Player of the Match: Anouar Ait El Hadj (Union Saint-Gilloise)
Matchday 2
01/10: Leverkusen vs PSV Eindhoven
01/10: Union Saint-Gilloise vs Newcastle (18:45)
Juventus 4-4 Borussia Dortmund
Borussia Dortmund and Juventus shared the spoils after an eight-goal thriller in Turin that equalled the record for highest-scoring Champions League draw. Khéphren Thuram and Loïs Openda both went close for the hosts in the first half, before Karim Adeyemi’s 52nd-minute finish sparked the encounter into life.
Kenan Yıldız, Felix Nmecha and Dušan Vlahović all scored in a four-minute flurry, before Yan Couto's powerful finish made it 3-2 to Dortmund. The visitors looked to have sealed victory through Ramy Bensebaini's 85th-minute penalty, but Juventus rescued a draw in added time thanks to Dušan Vlahović's finish and a Lloyd Kelly header.
Player of the Match: Dušan Vlahović (Juventus)
Matchday 2
01/10: Villarreal vs Juventus
01/10: Borussia Dortmund vs Athletic Club
All the league phase fixtures
Real Madrid 2-1 Marseille
A pair of penalties from Kylian Mbappé helped Real Madrid turn a deficit into victory in Xabi Alonso's first Champions League game at the helm. After withstanding early pressure from the hosts, Marseille struck first through Timothy Weah's emphatic finish, but Alonso's side were quickly level when Mbappé converted from the spot following a foul by Geoffrey Kondogbia on Rodrygo.
Although Madrid had Dani Carvajal sent off in the 72nd minute, Mbappé struck again with nine minutes left after Facundo Medina was penalised for handball.
Player of the Match: Kylian Mbappé (Real Madrid)
Matchday 2
30/09: Kairat Almaty vs Real Madrid (18:45)
30/09: Marseille vs Ajax
Benfica 2-3 Qarabağ
Qarabağ got their first-ever win in the Champions League proper with a famous comeback away at two-time European champions Benfica. The hosts raced into a 2-0 lead inside 16 minutes through Enzo Barrenechea and Vangelis Pavlidis, but Leandro Andrade pounced after a free-kick to get the Azerbaijani champions back in the game.
The visitors drew level shortly after the restart as Camilo Duran fired across Anatoliy Trubin and, while Benfica pushed to reclaim the advantage thereafter, it was Qarabağ who snatched a late winner through substitute Olexiy Kashchuk.
Player of the Match: Pedro Bicalho (Qarabağ)
Matchday 2 01/10: Qarabağ vs Copenhagen (18:45)
30/09: Chelsea vs Benfica
Tottenham 1-0 Villarreal
Highlights: Tottenham 1-0 Villarreal
UEFA Europa League holders Tottenham returned to the Champions League with a narrow 1-0 win over Villarreal. The hosts needed less than five minutes to score what proved to be the winner, Villarreal goalkeeper Luiz Júnior inadvertently directing Lucas Bergvall's cross into his own net.
Tajon Buchanan and Nicolas Pépé had chances to draw the visitors level, but Tottenham were relatively comfortable as they held on to mark Thomas Frank's managerial debut in the Champions League with a victory.
Player of the Match: Lucas Bergvall (Tottenham)
Matchday 2
30/09: Bodø/Glimt vs Tottenham
01/10: Villarreal vs Juventus
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