MONACO, Aug 24 (Reuters) - Holders Barcelona will play Chelsea for the third successive season after being placed together in the same opening-round group when the draw for the Champions League was made on Thursday.
Chelsea knocked Barcelona out 5-4 on aggregate at the first knockout round stage in 2004-05 but the Spanish giants exacted revenge by winning 3-2 on aggregate last season en route to winning the final against Arsenal in Paris in May.
Werder Bremen of Germany and Levski Sofia, the first Bulgarian team to take part in the competition proper, complete Group A.
Arsenal were handed a tough draw against 2004 European champions Porto and CSKA Moscow, winners of the UEFA Cup in 2005. Hamburg SV, European champions in 1983, complete Group G.
Manchester United will face Celtic in an all-British clash, with Benfica also in Group F. FC Copenhagen, who knocked Ajax Amsterdam out with a shock win in the third qualifying round, make their Champions League debut in the same group.
AC Milan, six-times winners of the European Cup, face Lille of France, AEK Athens and Anderlecht in Group H after UEFA sanctioned their participation despite their involvement in the Serie A match-fixing scandal.
Real Madrid, the record nine-times European champions, face Olympique Lyon, Dynamo Kiev and 1986 winners Steaua Bucharest in Group E.
• View the full Champions League group stage draw