The 24-year-old, nicknamed "Khalid the Cannibal" for his fierce tackling, joined the Blues after completing his medical assessment and agreeing personal terms with the west London giants over the weekend.

The fee has not been disclosed but is believed to be in the region of six million pounds (11.4 million dollars, 8.8 million euros).

The Dutchman, who can play anywhere across the defence, is available for Chelsea's Champions League campaign because he was a non-playing substitute in Hamburg's qualifying match against Osasuna.

He was at Stamford Bridge on Sunday to watch Chelsea kick off their attempt to win a third straight Premiership title with a 3-0 victory over visitors Manchester City.

Boulahrouz goes straight into the Chelsea squad for Wednesday's game at Middlesbrough, who lost 3-2 at Premiership debutants Reading on Saturday.

Blues boss Jose Mourinho is short of defenders with only Paulo Ferreira, Ricardo Carvalho, captain John Terry and Wayne Bridge available for the City game.

Geremi and Robert Huth are injured while William Gallas has been frozen out since returning late for pre-season training and talking publicly about his desire to leave.

that took a wicked deflection off Dunne and flew past the wrong-footed Nicky Weaver.

Georgios Samaras should have reduced the deficit just before half-time when he sprinted onto Sinclairs lobbed pass, but the Greek striker missed his kick completely with the goal at his mercy.

As well as excelling as a midfield anchor-man, Essien proved he has plenty to offer going forward when his long-range drive forced a fine save from Weaver.

Andriy Shevchenko was quiet on his Premiership debut but the Ukraine striker showed a glimpse of why Mourinho paid a British record 30 million pounds to sign him from AC Milan when he twisted away from Distin and fired in a shot that cannoned off Dunne to safety.

A dispiriting day for City took a turn for the worse when Corradi, a pre-season signing from Valencia, was sent off in the 63rd minute after his late lunge on Essien earned a second yellow card in quick succession.

Chelsea rarely needed to extend themselves after the break but were still able to extend their lead in the 79th minute.