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."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