Lionel Messi, taking his cue from Cristiano Ronaldo, plundered another hat-trick for Barcelona as goals again flowed freely in the Champions League on Wednesday.
The Argentine proved unstoppable in Barca's 4-0 hammering of Ajax Amsterdam as he became the first player to score four hat-tricks in Europe's elite club competition, taking his overall total to 62.
Ronaldo bagged a hat-trick in Real Madrid's 6-1 thrashing of Galatasaray on Tuesday when a record 30 goals rained in around the continent.
That flood turned into a trickle as only four goals were scored in the opening halves of the matches on Wednesday but the shackles were loosened later as the total for the first week rose to 53.
Jose Mourinho's first European tie since returning as Chelsea manager turned into a nightmare for the Portuguese as Swiss side Basel overturned a 1-0 halftime deficit at Stamford Bridge to win 2-1 in Group E.
Marco Streller scored Basel's late winner after Mohamed Salah had equalised for the Swiss who gained revenge for their defeat by Chelsea in the Europa League semi-finals last season.
"I'm not happy with the result," a crestfallen Mourinho said as Chelsea suffered their first defeat in 30 home group matches in the competition.
"Instead of moving a step forward towards qualification we have taken a step back."
Brazilian Oscar had scored for Chelsea on the stroke of halftime at an expectant Stamford Bridge as the first six goals of the night all came from south Americans.
Argentine Gonzalo Higuain opened his European account for Napoli as the Italians beat last year's runners-up Borussia Dortmund 2-1 in Group F. Arsenal beat Marseille 2-1 in the same group to continue their proud record of never having lost a European game away to a French club.
Former champions AC Milan and Porto both opened their group campaigns with wins. Milan beat Celtic 2-0 thanks to two late goals and Porto's Argentine midfielder Lucho Gonzalez sealed a 1-0 victory at Austria Vienna.
Also in Group G Brazilian Hulk scored for Zenit St Petersburg but his side lost 3-1 at Atletico Madrid.
Bundesliga side Schalke were frustrated for more than an hour by Steaua Bucharest but broke through late on with three goals to become early leaders of Group E.