Liverpool started their Champions League title defence in the worst possible way by losing 2-0 at Napoli while Barcelona survived a penalty to draw 0-0 at Borussia Dortmund.
Dries Mertens converted a penalty in the 82nd on Tuesday and Fernando Llorente struck in stoppage time for Napoli as the Italians beat their English opponents just as in last year's group stage.
Barcelona goalkeeper Marc-Andre ter Stegen parried Marco Reus' penalty and made several crucial saves as the five-time champions had a lucky escape in Dortmund in a second-half return of Lionel Messi from injury.
Chelsea's Ross Barkley meanwhile missed a late spot-kick in a 1-0 home defeat against Valencia while Norwegian teenager Erling Haland netted a first-half hat-trick as Salzburg routed Genk 6-2.
Last season's semi-finalist Ajax defeated OSC Lille 3-0, Inter Milan got a stoppage-time 1-1 against Slavia Prague, RB Leipzig won 2-1 at Benfica, and Olympique Lyon and Zenit St Petersburg drew 1-1.
