Borussia Dortmund maintained their 100 per cent start to the season with a 2-1 win over Krasnodar in the Europa League, courtesy of a late winner from Park Joo-ho.
The Russian side had taken the lead at Signal Iduna Park, and Thomas Tuchel's charges were far from their free-scoring best, but Matthias Ginter scored in first-half stoppage time to level the scores, before Park capped his full debut with a headed winner at the death.
The home side were three ahead by half-time after Callejon's chipped opener and Mertens' brace, and Marek Hamsik made it 4-0 before Callejon got in behind the Brugge back four to ensure the scoreline was emphatic.
Viktor Fischer cancelled out Nir Bitton's opener early on in the contest, but Celtic led again thanks to Mikael Lustig's headed goal.
Liverpool were held to a 1-1 draw in Bordeaux, where Adam Lallana's goal was cancelled out by Jussie's equaliser, and Lazio also failed to get off to a winning start despite Sergey Milinkovic-Savic's first goal for the club, as Yevhen Seleznyov's injury-time equaliser earned Dnipro a 1-1 draw in Dnipropetrovsk.
Elsewhere, Schalke won 3-0 at APOEL, Paulo Sousa's Fiorentina were beaten 2-1 at home by the coach's former club Basel, Villarreal lost 2-1 at Rapid Vienna, and Marseille were 3-0 winners at Groningen.
