Gareth Bale had a quiet start for Tottenham since returning to the London club, while Carlos Vinicius made a more impressive debut, setting up two goals in a 3-0 win over Lask in the Europa League on Thursday.
Arsenal opened their fourth straight Europa League campaign with a 2-1 come-from-behind win at Rapid Vienna in an opening round of games affected by Covid-19.
On a good night for Premier League clubs, Leicester earned a comfortable 3-0 home win over Zorya Luhansk.
Bale's second coming underwhelms - so far
After coming on as a substitute against West Ham for his first appearance since returning to Tottenham, Bale played more than an hour against in the Group J match against Austria’s Lask and had a hand in Tottenham’s second goal.
The on-loan forward collected a pass from Erik Lamela in the 27th minute and sent a low cross into the area from the right that defender Andres Andrade deflected into his own net.
Earlier, Lucas Moura finished off another free-flowing move to open the scoring after being set up by Vinicius.
The Brazilian created several other chances before teeing up substitute Son Heung-min to wrap up the win six minutes from time.
Tottenham manager Jose Mourinho is looking to win the competition for a third time with a third club, having won it with both Porto and Manchester United.
Substitutes galvanise Gunners' comeback
Arsenal went behind in their match when goalkeeper Bernd Leno played a poor pass that fell to Rapid forward Taxiarchis Fountas, who slotted in a low shot from a tough angle in the 51st minute.
Manager Mikel Arteta sent on Pierre Emerick Aubameyang and Hector Bellerín in the 61st, and the substitutes helped to spark the comeback.
After David Luiz headed in a free kick from Nicolas Pepe to level the score, Mohamed Elneny freed Bellerín down the right to cross for Aubameyang to complete Arsenal's comeback from close range.
Leicester's three points were a more assured affair.
James Maddison and Harvey Barnes scored first half-goals, and Kelechi Iheanacho added one more in the second in Group G as Brendan Rodgers’ team bounced back from two straight losses in the Premier League.
For once AC Milan didn’t need Zlatan Ibrahimovic to score, as Rade Krunic and Brahim Díaz netted in the first half at Celtic.
Substitute Jens Petter Hauge added the third for Milan in injury time after Celtic pulled one back through Mohamed Elyounoussi.
To pour further salt on The Hoops' wounds, Glasgow rivals Rangers won 2-0 at Standard Liege.
The highlight of the match was Kemar Roofe's opening goal, a shot from the halfway line that caught the goalkeeper off guard and looped into the net.
