Paris: Arsenal defeated Paris Saint-Germain 2-0 in their heavyweight Champions League clash on Tuesday, while last season's beaten finalists, Borussia Dortmund, delivered a brutal reality check to Celtic with an emphatic 7-1 victory in Germany.

Dortmund was the biggest winner on a night that also saw Barcelona, Manchester City, and Inter Milan secure comfortable victories, and Champions League debutants Brest winning 4-0 at Red Bull Salzburg.

The match between Arsenal and French champions PSG in London was the highlight of the day, marking the second round of matches in the new format of European football's elite club competition. The Gunners were deserving winners, with Kai Havertz heading in from a Leandro Trossard cross to open the scoring in the 20th minute. Bukayo Saka doubled their lead before half-time, as his free-kick delivery from the right evaded everyone 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 find a way back into the game. This marked Arsenal's first win in the Champions League this season, following a goalless draw away to Atlanta on matchday one two weeks ago.

"I’m 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."

Dortmund currently tops the 36-team league after following up a 3-0 win at Club Brugge in their first game with a decisive victory over Scottish champions Celtic in Germany. Karim Adeyemi scored a hat-trick in the first half for Dortmund, who led 5-1 at half-time. Emre Can opened the scoring from the penalty spot before Daizen Maeda equalized, but Adeyemi then took center stage. Serhou Guirassy added 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.

This represents Dortmund's biggest winning margin in the Champions League, matching their 6-0 win away to Legia Warsaw in 2016. "There's no such thing as a perfect game, but it was very, very good," Can said. "This has to be the standard we aim to set."

Barcelona defeated Swiss champions Young Boys 5-0, bouncing back from a 2-1 loss at Monaco two weeks prior and their first defeat of the season in La Liga last weekend against Osasuna. Robert Lewandowski scored twice, sandwiching goals from Raphinha and Inigo Martinez, before a late own goal by Mohamed Ali Camara capped the victory. "We knew after the game against Monaco that we had to respond quickly, and we did that well," Raphinha told broadcaster Movistar.

Winners of the Champions League in 2023, Pep Guardiola's Manchester City comfortably won 4-0 away to Slovan Bratislava in Slovakia, with goals from Ilkay Gundogan, Phil Foden, Erling Haaland, and James McAtee. Inter, who lost to City in the final in Istanbul two seasons ago, also won by the same scoreline at home to Red Star Belgrade. Hakan Calhanoglu opened the scoring with a stunning early free-kick, and Marko Arnautovic, Lautaro Martinez, and Mehdi Taremi—who scored from the penalty spot—added goals in the second half.

German champions Bayer Leverkusen secured their second straight win of the season, edging AC Milan 1-0 thanks to an early goal from Victor Boniface. Meanwhile, Brest, the French newcomers in the Champions League, also made it two wins out of two with a remarkable 4-0 victory away to Salzburg in Austria. Senegal striker Abdallah Sima, on loan from Brighton, scored twice, while Mahdi Camara and Mathias Pereira Lage also found the net, with Brest scoring three of their goals in just ten minutes during the second half.

Salzburg, Slovan Bratislava, and Young Boys currently occupy the bottom three positions in the early standings. VfB Stuttgart and Sparta Prague played to a 1-1 draw, with Enzo Millot putting the German side ahead before Finnish international Kaan Kairinen equalized before the interval. PSV Eindhoven and Sporting Lisbon also ended in a 1-1 draw, with Jerdy Schouten's opener for the Dutch champions canceled out by Daniel Braganca's late equalizer.