Real Madrid got their Champions League campaign on track with a 5-1 victory over Dynamo Kiev, while Manchester United ground out a 1-0 revenge win at Benfica on Tuesday.
Real, rocked by a 2-0 defeat in their Group E opener at Olympique Lyon two weeks ago, were 3-0 up at half-time after goals from Dutchman Ruud van Nistelrooy, captain Raul and Arsenal's on-loan forward Jose Antonio Reyes.
Raul and Van Nistelrooy each added another after the break as Real turned victory into a rout.
United, knocked out of last season's Champions League by a 2-1 group stage defeat at Benfica, had a stunning shot by French striker Louis Saha to thank for a scrappy victory at the Luz stadium in Group F -- their first away win in the competition for nearly three years.
Arsenal skipper Thierry Henry scored one and set up the other in a 2-0 home win over Porto that sent last season's finalists two points clear in Group G, following CSKA Moscow's 1-0 win over Hamburg SV.
Lyon, buoyed by their victory over Real, followed up with a 3-0 win at Steaua Bucharest, while Celtic shrugged off a defeat by United two weeks ago to beat FC Copenhagen 1-0.
There were no winners in Group H, where AC Milan had to settle for a 0-0 draw with Lille in northern France and AEK Athens finished 1-1 with Anderlecht in Greece.
CAPELLO'S VERDICT
Though satisfied with Real's result, their Italian coach Fabio Capello was none too impressed with his side's defending at the Bernabeu.
"We let them have too many chances and not all our opponents will be so generous to us...we made some defensive errors," Capello said.
Real and Steaua have three points apiece in a group led by Lyon on six.
"We are halfway to qualifying," said Lyon's delighted coach Gerard Houllier after goals from Brazilian forward Fred, Portuguese midfielder Tiago and substitute Karim Benzema sealed an emphatic victory in the Romanian capital.
United, who became England's first European Cup winners by beating Benfica in 1968, will feel they too are on course after settling their more recent score with the Portuguese side.
Having beaten Celtic 3-2 two weeks ago at Old Trafford, Saha's superb left-foot shot from the edge of the area leaves United with maximum points from two games.
Striker Kenny Miller converted a penalty to give Celtic a 1-0 win over FC Copenhagen and second place in the group.
Arsenal were convincing at the Emirates Stadium, reaching six points with some slick passing and two clinical finishes from midfielder Alexandr Hleb and Henry in the night's other Anglo-Portuguese contest.
"The team has a lot of potential and is getting stronger in every game," Arsenal manager Arsene Wenger said after his side saw off the 2004 Champions League winners.
Milan coach Carlo Ancelotti was sanguine about the six-times European champions being held by a Lille side whose ground is not up to UEFA standards and who have to play at Lens.
"It was not an easy match," said Ancelotti. "I am satisfied with our display... we have had opportunities."
