By Phil McNulty

Michael Ballack celebrates scoring Chelsea's second from the spot

Chelsea survived anxious moments against Werder Bremen to open their Champions League campaign with a win.

Michael Essien put Chelsea ahead after 23 minutes following a stumble by Bremen defender Petri Pasanen.

Bremen hit back after the break, with World Cup leading scorer Miroslav Klose heading over from eight yards and then hitting the bar with another header.

Michael Ballack eased Chelsea's nerves from the spot after 66 minutes when Clemens Fritz fouled Didier Drogba.

News conference: Chelsea boss Jose Mourinho

The only downside of a satisfying night for Jose Mourinho's side were cheap bookings picked up by John Terry, Frank Lampard, Joe Cole and Drogba.

Essien was outstanding in the first 45 minutes, and his influence was seen early on when his cross was headed narrowly wide by Drogba.

And he was only inches away from a crucial touch at the near post after Andriy Shevchenko escaped down Bremen's left flank.

But the Ghanaian midfield man made no mistake after 23 minutes when he took advantage of a mistake by central defender Pasanen to give Chelsea the lead.

Pasanen slipped under pressure from Lampard and the ball ran loose for Essien to beat Andreas Reinke from just inside the area.

Bremen opened the second half with a greater sense of purpose and the normally lethal Klose wasted the perfect opportunity to restore equality eight minutes after the break.

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Torsten Frings served up the perfect cross and Klose rose well but headed off target from only eight yards.

Chelsea responded with a cross from Ashley Cole that was volleyed into the side-netting by Drogba - before Bremen came even closer to an equaliser after 64 minutes.

Frings was the provider again with another right-wing cross, and this time Klose's looping header bounced to safety off the crossbar.

But just as Bremen threatened to surprise Chelsea, Clemens Fritz needlessly fouled Drogba to concede a penalty.

Ballack took over penalty duties from Lampard, who missed against Charlton, and demonstrated his expertise by lashing an unstoppable finish high past Reinke.

Lampard was almost on target from open play with 11 minutes left, firing in a shot from a tight angle that struck an upright.

Chelsea: Cech, Boulahrouz, Terry, Ricardo Carvalho, Ashley Cole, Essien, Makelele, Ballack (Mikel 90), Lampard, Shevchenko (Joe Cole 81), Drogba (Kalou 85).
Subs Not Used: Cudicini, Geremi, Bridge, Paulo Ferreira.Booked: Terry, Drogba, Lampard, Joe Cole.

Goals: Essien 24, Ballack 68 pen.

Werder Bremen: Reinke, Wome, Naldo, Pasanen, Fritz, Borowski, Baumann (Zidan 86), Frings, Diego, Klasnic (Hugo Almeida 65), Klose.
Subs Not Used: Kasper Jensen, Vranjes, Owomoyela, Andreasen, Schulz.Booked: Baumann.

Att: 32,135

Ref: Kyros Vassaras (Greece).