Paris - Gareth Bale got his season up and running with two goals before being sent off as Real Madrid drew at Villarreal, while Kalidou Koulibaly's howler gifted Juventus a thrilling victory over Napoli.
Elsewhere, Borussia Dortmund slipped up but Atletico Madrid continued their strong start as Monaco's woes continued.
Here, AFP Sport takes a look at five main talking points from the weekend in European football:
Dortmund title credentials in question
After coming within a whisker of winning the title last year and signing several top players in the transfer window, this was supposed to be the season in which Borussia Dortmund finally toppled Bayern Munich in the Bundesliga.
Yet Saturday's 3-1 defeat by Union Berlin has prompted fresh doubts over whether Lucien Favre's side have the mental strength to win the league.
After picking up eight goals and six points from their opening two games, Dortmund were brought down to earth with a bump in Berlin, outfought and outclassed by a newly-promoted side with no previous Bundesliga experience.
"We were stupid. We need to stop thinking we can win games with quality alone," raged captain Marco Reus.
Coach Favre, meanwhile, criticised the club's official line that Dortmund are title contenders this year.
"We have to be careful what we say. We have a lot to do," said the Swiss.
New-look Atletico threatening La Liga push
Atletico Madrid were supposedly in crisis at the end of last season, their best player about to be sold and several others soon to follow.
Yet three games into the new campaign and Diego Simeone's side sit top of La Liga, with belief growing in Spain they can not only challenge for the title but win it.
Without Antoine Griezmann and with Joao Felix, they came from two goals down to beat Eibar 3-2 on Sunday and move five points clear of defending champions Barcelona. The season is young but Atleti have nine points out of nine. It is a strong start.
Doubts over De Ligt?
Dutch international defender Matthijs De Ligt had a nightmare debut for Juventus as lapses by the €75-million ($82.4 million) signing allowed Napoli to fight back from three goals down in a 15-minute second-half spell in Turin.
The former Ajax captain made his first start with Giorgio Chiellini out injured, but only a Kalidou Koulibaly own goal allowed Juventus to snatch a last-gasp 4-3 win.
"At 3-0 we felt sated and we allowed Napoli to come back," said Juve assistant coach Giovanni Martusciello.
"De Ligt comes from a team that defended differently, in a league that is not the Italian one. He also played well for an hour, then his condition was lacking a bit. But he is a player of the highest level."
Benfica and Porto have won the last 17 Portuguese league titles between them, but little Famalicao are showing that the division can produce unlikely success stories too.
The team, who slipped into the fifth division in 2008, were promoted to the top flight for the first time since 1994 by finishing second in the LigaPro last term.
They have taken the Primeira Liga by storm so far, though, and are the only unbeaten team left after four games.
With Benfica, Porto and Sporting all having already lost this term, a thrilling 3-2 win at Aves on Saturday was enough to send Famalicao to the top of the table.
More misery for Monaco
Monaco's dreadful form is showing no sign of improving after the 2017 French champions' winless start to the season continued with a 2-2 draw at Strasbourg.
The return of Leonardo Jardim after Thierry Henry's brief, and ill-fated, spell as coach precipitated a short revival last term which was ultimately just enough to stave off relegation.
But their form suffered at the end of last season and the poor start to the current campaign means Monaco have now won just one of their last 13 Ligue 1 matches.
Captain Radamel Falcao has moved to Istanbul to join Galatasaray, and despite close-season signing Islam Slimani's strong form, there is little sign that this season will be much better than the last for the principality club.