London - Chelsea maintained their 100 percent start to the Premier League season as Michael Essien's double-strike inspired a 3-1 win over struggling West Ham at Upton Park on Saturday.
Carlo Ancelotti's side have scored 17 goals this season in their four consecutive victories, although they were helped on this occasion by another high-profile error from Hammers goalkeeper Robert Green.
Essien had headed the champions into an early lead before Green gifted the second to Kalou with a mistake that had echoes of his blunder playing for England at the World Cup against the United States.
Ghana midfielder Essien added another late on before Scott Parker reduced the deficit for West Ham, who remain rooted to the bottom of the table after four straight defeats, with two goals scored and 12 conceded.
Chelsea had the luxury of resting Florent Malouda ahead of their Champions League trip to face MSK Zilina on Wednesday, with their in-form winger on the bench.
It mattered little as they were ahead in the second minute through Essien's header from Didier Drogba's corner.
Chelsea midfielder Ramires, making his debut following his transfer from Benfica, won the set-piece with a powerful run from deep.
Drogba swung over the corner and Essien climbed between Mark Noble and Herita Ilunga to head past Green, despite the efforts of Carlton Cole on the line.
It was Essien's first goal of the campaign, with his previous strike coming on his final appearance last season before he suffered a serious knee injury.
The goal allowed the champions to play at their own pace and they were happy to sit on their lead, only for Green to gift them a second with his poor handling.
Drogba's 25-yard free-kick was straight at Green and also lacked power, but it was spilled into open play. Matthew Upson could have punted the ball clear but his clearance struck Kalou and looped in.
It capped a frustrating week for Upson after he was included in the England squad for their European Championship qualifiers but was not on the bench for either victory.
Upson did prevent Kalou grabbing a third when he made a last-ditch tackle, but Chelsea were firmly in control by then.
John Obi Mikel also struck the crossbar with a powerful volley before the break as the Blues looked increasingly likely to add to their advantage.
West Ham striker Victor Obinna, on his debut after being loaned from Inter Milan, was the hosts' only serious goal threat.
Cole chipped through for Obinna and he planted his finish wide, then he cut inside and was off-target with his angled drive.
Cole also had an effort disallowed for offside but they could not reduce the deficit before the interval and Avram Grant made his move by bringing on Kieron Dyer to replace Luis Boa Morte for the second half.
But it was proving tough to break down a Chelsea defence who had not conceded a Premier League goal in the first three matches of the season.
In fact, Chelsea looked like scoring on the counter-attack, firstly when Ramires tried his luck when West Ham defenders were backing off.
Then Kalou cut in from the right flank and curled an effort just wide of Green's post, while Drogba had an effort saved when his shot was heading into the bottom corner.
Essien's second goal came with seven minutes left as he headed in from Paulo Ferreira's cross.
Parker pulled one back with a deft lob after Cech punched a corner clear but it was too little too late for West Ham, who also saw Frederic Piquionne miss a sitter.