Sergio Ramos scored Real Madrid's first goal against Steaua
Lyon maintained their perfect start in Group E with a 3-0 win over bottom side Dynamo Kiev - who are as good as out after losing their first three matches.
Juninho and Kim Kallstrom put Lyon ahead before half-time before Florent Malouda's header completed the scoring.
Real Madrid also impressed on the road, thrashing Steaua Bucharest 4-1.
Sergio Ramos, Raul and Robinho put Real in control and although Valentin Badea pulled one back, Ruud van Nistelrooy's neat chip made sure of victory.
David Beckham came on as a substitue to make his 100th Champions League appearance. He is third in the all-time standings for most appearances in the competition, behind only Raul and Roberto Carlos.
Kenny Miller netted twice as Celtic took a huge step towards qualifying for the knockout stages for the first time with a convincing victory over Benfica.
Stephen Pearson rounded off the scoring to give his side a deserved 3-0 win.
Manchester United comfortably beat FC Copenhagen, with Paul Scholes, John O'Shea and Kieran Richardson all netting in a 3-0 win at Old Trafford.
If Celtic beat Benfica in Portugal in their next game and Manchester United draw in Denmark, both will progress.
Arsenal saw their 100% winning record in Group G disappear as they lost out to CSKA Moscow in Russia.
Daniel Carvalho scored the only goal of the game for CSKA with a powerful free-kick - and they move above the Gunners to the top of the table.
FC Porto claimed their first Champions League win of the season with a thumping 4-1 victory over SV Hamburg.
Lisandro Lopez (2), Lucho Gonzalez and Helder Postiga put Porto in control before Piotr Trochowski's consolation.
Kaka celebrates his winner for AC Milan against Anderlecht
AC Milan stayed top of Group H after Kaka's winner against Anderlecht.
Milan had Daniele Bonera sent off at the start of the second half but they responded well and Kaka smashed home a superb drive to give them the points.
Lille are in second place after they hit two late goals to see off winless AEK Athens 3-1.
Mathieu Robail put Lille ahead before Vladimir Ivic equalised - but Daniel Gygax and Jean Makoun scored in the last 10 minutes for the French side.