Chelsea got their UEFA Champions League campaign off to a winning start with a 2-0 victory over Werder Bremen at Stamford Bridge, but it was far from plain sailing for Jose Mourinho's side.

Goals from Michael Essien and Michael Ballack proved sufficient for the Premiership champions, but each one owed much to individual errors from the visiting side.

Defender Petri Pasanen presented Essien with the first and Ballack then rifled in the decisive second from the penalty spot after Clemens Fritz had needlessly fouled Didier Drogba.

Otherwise it was an even contest and the German side had their chances, notably from Miroslav Klose, the top scorer at this summer's World Cup.

Despite the excellence of Ricardo Carvalho and John Terry at the heart of the Chelsea defence, Klose was a constant aerial threat, going close with two headed chances as the hosts were put under severe pressure after the interval.

Essien was the game's outstanding player in the early stages and he had already created a decent scoring opportunity for Drogba - which he headed wide - and flashed a shot past a post before putting his side ahead.

Frank Lampard's driving run through the centre was interrupted by Frank Baumann, but Pasanen slipped when the ball ricocheted to him and Essien was left in the clear to stroke in the opener.

Chelsea failed to build on their advantage, though, and Werder gradually got back into the game and they almost levelled when Klose cut in from the left and fired in a shot which Carvalho diverted wide for a corner.

The visitors then grew in stature after the break, with Fritz and the excellent Torsten Frings keeping Ashley Cole quiet on his full debut for The Blues.

Germany international Frings twice teed up chances for Klose with right-wing crosses, but the first was wasted before the tall striker looped a header onto the crossbar with Petr Cech beaten.

In between Tim Borowski tested Cech with a rising drive from 20 yards before Chelsea were awarded the penalty which enabled them to kill off the game.

Drogba was pushed in the back by Fritz as he climbed for a header and, with Lampard having missed from 12 yards against Charlton at the weekend, Ballack hammered in the second.

Lampard could have added a third when he turned sharply in the area and angled a shot against the inside of the far post, but a three-goal margin of victory would have flattered the hosts.

Chelsea	Team Statistics	Werder Bremen
2	Goals	0
1	1st Half Goals	0
5	Shots on Target	2
5	Shots off Target	9
1	Blocked Shots	4
4	Corners	5
17	Fouls	11
4	Offsides	2
4	Yellow Cards	1
0	Red Cards	0
86.2	Passing Success	82
23	Tackles	29
39.1	Tackles Success	86.2
54.4	Possession	45.6
43.9	Territorial Advantage	56.1