Napoli remain top of Group E in the Champions League despite being held to a goalless draw at Genk on Wednesday might.
The Partenopei - who beat Champions League holders Liverpool 2-0 at home in their opening match - had started brightly in Belgium, but were not able to find a breakthrough as Genk recovered from their 6-2 trashing in Salzburg.
Liverpool saw off a remarkable fightback from Red Bull Salzburg to win their clash 4-3 at Anfield.
Sadio Mane had given the Reds a ninth-minute lead against his former club after a one-two with Roberto Firmino.
Full-back Andrew Robertson finished off a sweeping move to make it 2-0 in the 25th minute.
Mohamed Salah added a third on 36 minutes, tucking home a parry from the Salzburg goalkeeper.
The visitors pulled a goal back on 39 minutes when Hwang Hee-chan lashed in an angled shot.
Takumi Minamino's fine volley at the far post made it 3-2 in the 56th minute.
The visitors completed the comeback on the hour when substitute Erling Braut Haaland scored his 18th goal of the season from close range.
Salah, though, had the final say when he collected a flicked header from Firmino to score Liverpool's fourth with 20 minutes left.
In Group F, Barcelona recovered from a slow start to beat Inter Milan 2-1 at the Nou Camp with a brace from Luis Suarez.
Inter had taken the lead after just two minutes when Lautaro Martinez was put clear by Alexis Sanchez after Gerard Pique lost possession on the halfway line.
The Italians then saw an effort from Antonio Candreva ruled out for offside.
Luis Suarez drew Barcelona level just before the hour with an acrobatic effort.
With six minutes left, Lionel Messi - fit enough to start - surged forwards before picking out the Uruguay forward to fire in a winner.
Borussia Dortmund won 2-0 at Slavia Prague, with two goals from full-back Acham Hakimi, to put the Germans top of Group F on goal difference.
Stanislav Tecl had squandered the chance to equalise in the second half when through on goal, only to shoot into the side netting before Hakimi sealed victory with another well-taken late effort.
Chelsea recorded their first win in Group H as they battled to a 2-1 victory in Lille.
Forward Tammy Abraham marked his 22nd birthday with the opening goal in the 22nd minute when he beat the offside trap.
Victor Osimhen, though, equalised in the 33rd minute from a corner, before Chelsea midfielder Jorginho hit the frame of the goal ahead of half-time.
Willian scored the winning goal in the 78th minute as Frank Lampard's men recovered from the opening home defeat by Valencia.
The Spaniards, meanwhile, were beaten 3-0 at home by Ajax, who have a 100% start.
Hakim Ziyech's spectacular effort broke the deadlock on eight minutes.
Daniel Parejo then missed a chance to equalise when he sent a penalty over the bar in the 25th minute.
Quincy Promes added a second before half-time, with Donny Van De Beek scoring a third in the 67th minute for last season's semi-finalists.
In Group G, Zenit St Petersburg beat Lyon 3-1 at home to top the table.
Artem Dzyuba put the Russians ahead in the 22nd minute, with an own goal from Ruben Dias given following a VAR review and Sardar Azmoun's solo effort wrapping things up. Raul De Tomas scored a late consolation.
Memphis Depay was on target as Lyon won 2-0 at RB Leipzig, with Martin Terrier also scoring in the second half.