Liverpool and Barcelona both scored wins in their opening Uefa Champions League games while Tottenham Hotpur were beaten.
Roberto Firmino struck a stoppage-time winner as Liverpool beat Paris St Germain 3-2 at Anfield.
PSG had come back from two goals down with Kylian Mbappe equalising in the 83rd minute, but then Firmino, who started on the bench due to an eye injury, drilled home a low shot in the final seconds.
Daniel Sturridge, in for Firmino, had opened the scoring for an impressive Liverpool in the 30th minute with a fine header from an Andy Robertson cross.
Six minutes later last season's Champions League runners-up doubled their lead when PSG defender Juan Bernat tripped Georginio Wijnaldum in the area and James Milner slotted home the penalty.
The Parisians got themselves back into the game though five minutes before the break when Robertson failed to clear and Thomas Meunier drove home a first-time effort.
Then Mbappe stunned the raucous Anfield crowd with a clinical finish only to see Firmino grab the glory.
Lionel Messi scored a record eighth Champions League hat-trick as Barcelona kick-started their campaign with a 4-0 home win over PSV Eindhoven.
The Spanish champions' all-time top scorer Messi broke the deadlock in the 32nd minute with an immaculate free kick which he curled over the wall into the top corner against a PSV side who had defended well and looked dangerous on the break.
But Barca demonstrated the gulf in class as the second half progressed and doubled their lead in the 75th with a curling strike from French forward Ousmane Dembele, who scored his fifth goal in six games in all competitions this season.
Messi got his second two minutes later when he turned Ivan Rakitic's dinked pass into the net with a flick of his boot.
The mood was briefly dampened when Barca's France defender Samuel Umtiti was dismissed in the 79th for a second yellow card before Messi completed his treble three minutes from time.
The Argentine received another chipped pass, this time from Luis Suarez, and ruthlessly smashed the ball home.
The strike completed eight trebles in Europe's top competition for Messi, one more than rival Cristiano Ronaldo who will make his Juventus Champions League debut tomorrow.
Inter Milan staged a late smash-and-grab raid as goals by Mauro Icardi and Matias Vecino secured a 2-1 home win over Tottenham Hotspur.
Spurs appeared to have delivered the perfect response to their stuttering domestic form as they led through Christian Eriksen's deflected 53rd-minute strike.
Inter, who have started poorly in Serie A, were offering little threat but Icardi's superb 86th minute volley brought the San Siro to life and Vecino's stoppage-time header left Tottenham crestfallen at the final whistle.
The surprising late turnaround condemned Spurs to a third consecutive defeat for the first time since Mauricio Pochettino took charge in 2014.