Chelsea's annual pursuit of the continent's biggest club prize that has so far eluded them began in encouraging fashion for the latest coach in the hot seat as Andre Villas-Boas' team beat Bayer Leverkusen 2-0 in Group E.
The other Anglo-German tussle among the eight matches in Groups E-H ended in a 1-1 draw between Bundesliga champions Borussia Dortmund and Arsenal in northern Germany.
While Chelsea and Arsenal still seek a first Champions League crown, former European champions Porto and Olympique Marseille began with victories.
Porto beat Shakhtar Donetsk 2-1 in Group G although they were helped by their Ukrainian opponents having two players sent off -- Yaroslav Rakitskiy for a straight red card in the 40th minute for a poor tackle and Dmytro Chygrynskiy for a second booking late on.
In Group F, French side Marseille edged out Olympiakos Piraeus 1-0 in Greece. Newcomers Viktoria Plzen got their first point on the board with a 1-1 draw at home to BATE Borisov of Belarus, although with Barcelona and Milan waiting in Group H, life is about to get much tougher for the Czechs. The stand-out fixture of the night in the Nou Camp exploded into life when Milan's Alexandre Pato surged through a flat-footed Barca backline to score the fifth-fastest goal in the competition, timed at 24 seconds.
It took Barcelona a while to clear their heads but the Catalans went level before half time when Lionel Messi, top scorer in the competition for the past three years, turned provider with a perfect cut back for Pedro to tap in. David Villa's sublime curling free-kick after 50 minutes put Barca in front and, with their striker Zlatan Ibrahimovic missing through injury, Milan rarely threatened to get back on level terms. However, the Serie A champions struck again at the death when Thiago Silva rose above the home defence to head home from a corner in the second minute of stoppage time.
A frustrating night for Barca was summed up by a leg muscle injury sustained by midfielder Andres Iniesta that will keep him out for four weeks. Iniesta was replaced before half time by new signing Cesc Fabregas.
Chelsea welcomed back Michael Ballack to Stamford Bridge but it was not to be a happy return for the German midfielder as goals by Brazil defender David Luiz and Spain forward Juan Mata gave Villas-Boas the perfect start to the campaign.
Both goals were set up by Spain striker Fernando Torres, recalled to the side after being left out of Chelsea's Premier League victory at the weekend because of poor form.
Arsenal looked on course for a notable win at Borussia Dortmund, thanks to Robin van Persie's clinical finish just before half time, but a stunning 88th-minute volley by Ivan Perisic denied the Gunners, whose manager Arsene Wenger had to watch the match from the stands because of a touchline ban.
