Kalou struck in the 55th minute at Upton Park but it needed Cech to save Mark Noble's penalty to keep the Blues ahead and send them into European action in high spirits.
The celebrations for Kalou's goal were marred by objects being thrown in the direction of Frank Lampard and John Terry, although that is hardly likely to affect a Chelsea team that is focused on ending its season with silverware.
They started the weekend six points behind Premier League leader Manchester United and Guus Hiddink, in charge until the end of the season, has given up hope of catching up.
With that in mind, this match served to tee-up their clash at the Nou Camp on Tuesday, with Didier Drogba, Michael Essien and Michael Ballack on the bench.
Ashley Cole was also among the substitutes and, as he was suspended for the Barca clash, Jose Bosingwa was given a dry run in the position ahead of facing Lionel Messi. Luis Boa Morte was his sparring partner three days before the heavyweight clash in Spain.
There were reunions in the dug-out and on the pitch, with Hammers manager Gianfranco Zola and assistant Steve Clarke facing their former club.
Both were poised to announce long-term deals at West Ham following a successful first season together, with West Ham still in the hunt for a place in the Europa League despite this defeat.
For the visitors, midfielder Lampard was given his usual hostile welcome from West Ham fans who are still bitter after he left in 2001, while Terry was not spared either.
England's captain spent five years at the Hammers' academy before joining Chelsea as a 14-year-old, and there were poisonous chants from the home fans towards the centre-back.
It was Lampard who created the first chance, in the 16th minute, when he slid the ball through to Florent Malouda - but the Frenchman dragged his shot wide after racing through.
Kieron Dyer, making his first start since August 2007, should have given the hosts a lead shortly after but he shot tamely at Cech after Diego Tristan had split the Chelsea defence.
Lampard, with jeers ringing in his ears, had a few sighters on Robert Green's goal. One volley flashed wide, a second went straight at the West Ham goalkeeper and Noble bravely blocked another.
Chelsea was applying pressure but almost fell behind just before the break. John Mikel Obi was needed to clear off the line when Tristan prodded towards goal after Noble's corner was nodded down by Matthew Upson and Cech was out of position.
After that scare, the visitors were ahead 10 minutes after the restart.
Lampard wriggled to the byline down the left and floated a cross to the far post, where Kalou took one touch before planting his finish into the empty net for his ninth of the season.
Lampard and Terry celebrated in front of the Bobby Moore Stand and missiles were thrown towards them from the crowd, an incident the Football Association could now look at.
Bosingwa was given a breather just before the hour mark, with Cole coming on at left-back, while Zola's response to falling behind was replacing Dyer and David di Michele with Freddie Sears and Radoslav Kovac.
Nicolas Anelka should have doubled the lead when Juliano Belletti sent him through after Upson slipped, with Green rushing out to block the finish. Cole then shaved the crossbar after exchanging passes with Malouda.
The Hammers were given their penalty 20 minutes from full-time when Herita Illunga's shirt was pulled by Kalou.
Noble's penalty was struck well but Cech leapt to his left and tipped away the effort.
That was the closest the Hammers got to an equaliser as Chelsea held on for a confidence boosting win before going to the Nou Camp.