Arsenal beat Paris Saint-Germain 2-0 in their heavyweight Champions League duel on Tuesday, while last season's beaten finalists Borussia Dortmund gave Celtic a brutal reality check with an emphatic 7-1 win in Germany.
Dortmund were the biggest winners on a night which also saw Barcelona, Manchester City and Inter Milan claim one-sided victories and Champions League debutants Brest won 4-0 at Red Bull Salzburg.
The clash between Arsenal and French champions PSG in London was the big game of the day as the second round of matches in the new format of European football's elite club competition got underway.
The Gunners were worthy winners with Kai Havertz heading in from a Leandro Trossard cross to open the scoring on 20 minutes and Bukayo Saka doubling their lead before half-time as his free-kick delivery from the right evaded everybody on its way in.
PSG saw Nuno Mendes strike the outside of the post from range in the first half while Joao Neves hit the woodwork after the break, but the visitors could not get back into the game.
It is a first win in the Champions League this season for Mikel Arteta's Arsenal, who drew 0-0 away to Atalanta on matchday one two weeks ago.
"Really, really happy with the performance," Arteta told broadcaster Amazon Prime. "The Champions League brings different demands but I think we handled it really well."
Adeyemi hat-trick
Dortmund are currently on top of the 36-team league after they followed a 3-0 win at Club Brugge in their first game by trouncing Scottish champions Celtic in Germany.
Karim Adeyemi scored a hat-trick in the first half for Dortmund, who were 5-1 ahead at half-time. Emre Can opened the scoring from the penalty spot before Daizen Maeda equalised, but Adeyemi then took centre stage.
Serhou Guirassy netted a penalty before the interval and made it 6-1 midway through the second half, with substitute Felix Nmecha wrapping up the victory late on.
It is Dortmund's biggest winning margin in the Champions League alongside a 6-0 win away to Legia Warsaw in 2016.
"There's no such thing as a perfect game, but it was very, very good," said Can. "This has to be the standard we aim to set."
Barcelona, Man City win
Barcelona beat Swiss champions Young Boys 5-0 to bounce back from a 2-1 loss at Monaco a fortnight ago and their first defeat of the season in La Liga last weekend at Osasuna.
Robert Lewandowski scored twice either side of goals by Raphinha and Inigo Martinez before a late Mohamed Ali Camara own goal wrapped up the victory.
"We knew after the game against Monaco in the Champions League we had to give a quick reply in the next game, which was this one, and we did that well," Raphinha told broadcaster Movistar.
Winners of the Champions League in 2023, Pep Guardiola's City were comfortable 4-0 winners away to Slovan Bratislava in Slovakia, with Ilkay Gundogan, Phil Foden, Erling Haaland and James McAtee getting the goals.
Inter, who lost to City in the final in Istanbul two seasons ago, won by the same scoreline at home to Red Star Belgrade.
Hakan Calhanoglu set Inter on their way with a stunning early free-kick before Marko Arnautovic, Lautaro Martinez and Mehdi Taremi all netted in the second half, the latter from a penalty.
German champions Bayer Leverkusen got their second straight win in this season's competition as a Victor Boniface goal early in the second half allowed them to beat AC Milan 1-0.
Brest surprise
Meanwhile Brest, the French Champions League newcomers, also made it two wins out of two with a remarkable 4-0 victory away to Salzburg in Austria.
Senegal striker Abdallah Sima, the forward on loan from Brighton who got their winner against Sturm Graz two weeks ago, scored twice.
Mahdi Camara and Mathias Pereira Lage also found the target with Brest scoring three of their goals in the space of 10 second-half minutes.
Salzburg, Slovan Bratislava and Young Boys are the bottom three in the early standings.
VfB Stuttgart and Sparta Prague drew 1-1 with Enzo Millot putting the German side ahead and Finnish international Kaan Kairinen equalising before the interval.
PSV Eindhoven and Sporting Lisbon also drew 1-1. Jerdy Schouten's opener for the Dutch champions was cancelled out by Daniel Braganca's late leveller.
