Robert Lewandowski got the 82nd-minute winner as Borussia Dortmund put the brakes on Arsenal's campaign with a 2-1 win in London that, along with Napoli's 2-1 victory at Olympique Marseille, put three teams on six points in Group F.
Lionel Messi marked his first start after injury with a goal in Barcelona's 1-1 draw at AC Milan in the Champions League on Tuesday while Fernando Torres got two as Chelsea thumped Schalke and Atletico Madrid's charge continued.
There is a clear leader in Group G, where Atletico made it three wins from three with a 3-0 victory at Austria Vienna that left them a point away from the 10 that are usually enough to send teams into the last 16 of Europe's elite club competition.
With Diego Costa scoring twice, including a stunning solo effort, they went five points clear of second-placed Zenit St Petersburg, who made the most of the sixth-minute sending off of Porto's Hector Herrera - the competition's fastest ever dismissal from two yellow cards - to beat their hosts 1-0.
In Group E, Chelsea moved level on six points with Schalke 04 at the top with a 3-0 win in Germany where Torres celebrated his 100th start for the club with the fifth-minute opener and another after 69 minutes before Eden Hazard added a late goal.
The top two are clear of third-placed Basel, who have four points ahead of Steaua Bucharest on one after those two teams shared the spoils in a 1-1 draw in Romania.
Celtic got their first points in Group H after a James Forrest penalty on the stroke of halftime and a deflected shot by Beram Kayal early in the second half helped them to a 2-1 win over Ajax Amsterdam, who got a consolation in added time.
Barca are in charge of that group with seven points, while Milan - who had gone ahead through Robinho's ninth-minute opener before Messi levelled after 23 minutes - have five points. Celtic are on three points with Ajax bottom on one.
The day's biggest statement of intent came from 2012 European champions Chelsea, who have now made amends for the