On a dramatic opening night of the league phase, Juventus and Borussia Dortmund played out a thrilling 4-4 draw and Benfica surrendered a two-goal lead to lose.
Meanwhile, Kylian Mbappe scored two penalties as 10-man Real Madrid came from behind to launch their latest Champions League campaign with a hard-fought 2-1 win over Marseille.
Premier League rivals Arsenal and Tottenham both made winning starts against Spanish opposition in Athletic Bilbao and Villarreal respectively.
Spanish giants Real, chasing a record-extending 16th European title, fell behind to a Timothy Weah strike in a compelling encounter at the Bernabeu but Mbappe quickly levelled from the spot.
Real’s task got tougher when Dani Carvajal – an early replacement for Trent Alexander-Arnold, who suffered a hamstring injury just four minutes in – was sent off for headbutting Marseille goalkeeper Geronimo Rulli.
But Mbappe had the final say nine minutes from time after Facundo Medina was penalised for handball.
Dusan Vlahovic and Englishman Lloyd Kelly both scored in stoppage time as Juventus snatched a dramatic 4-4 draw against Dortmund.
All eight goals came in the second half with Dortmund striking first through Karim Adeyemi.
Kenan Yildiz levelled but Dortmund went ahead again when Felix Nmecha found the net.
Vlahovic scored another equaliser but the Germans looked set to win after opening up a 4-2 lead through a Yan Couto drive and a Ramy Bensebaini penalty.
Yet Juve were not finished as Vlahovic and Kelly netted late on.
The Gunners won 2-0 in Bilbao after second-half goals from substitutes Gabriel Martinelli and Leandro Trossard.
Martinelli scored just 36 seconds after coming off the bench in the 71st minute and then turned provider for Trossard to wrap up victory three minutes from time.
Spurs benefited from a freak only goal after just four minutes as they beat Villarreal 1-0 at the Tottenham Hotspur Stadium.
Villarreal goalkeeper Luiz Junior spilled Lucas Bergvall’s cross into his own net in comical fashion after just four minutes and the goal proved enough. Former Arsenal midfielder Thomas Partey was a late Villarreal substitute, ahead of a court appearance on rape charges in London on Wednesday.
Qarabag of Azerbaijan produced a stunning result to win 3-2 at Benfica, who looked on course for a comfortable win after goals from Enzo Barrenechea and Vangelis Pavlidis in the first 16 minutes.
Leandro Andrade, Camilo Duran and Oleksii Kashchuk scored in a remarkable fightback.
Belgian champions Union St Gilloise enjoyed a dream debut in the competition as they pulled off a shock 3-1 win at PSV Eindhoven.
Promise David opened the scoring with an early penalty and Anouar Ait El Hadj ran half the length of the field to double the lead before Kevin Mac Allister bundled in a late third.
Ruben van Bommel scored a 90th-minute consolation for the hosts.
