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.