A first half goal from Ramires gave the visitors the lead at the interval, but Jelle Vossen struck for the Pro League side on the hour mark to square things up.
Andre Villas Boas switched his team around slightly, with Frank Lampard and Juan Mata starting from the bench, and Oriol Romeu and Raul Meireles starting. Under-fire centre back John Terry was an unused substitute.
After the result Villas Boas tried to remain positive.
“The first half was good, we managed to get the goal we wanted, the second half we went down a level, in the first 20 minutes we could have had more control of the game,” he told Sky Sports.
“I think we had fantastic opportunities to win the game but it just didn’t happen, we have to get these opportunities in the back of the net. This is the most important thing in a football game.
“We created a lot of attacking opportunities and we will be able to get the momentum back we had before (the defeat to) Queens Park Rangers. At the moment it is not happening for us.
“Not everything is negative but we could have done better,” he concluded.
In the other fixture in Group E, Valencia got revenge on Bayer Leverkusen at the Mestalla, beating their conquerors from two weeks ago 3-1, and bringing themselves right back into contention.
An early strike by Jonas was cancelled out by Stefan Kiessling to see the game go into the break all square, but second half goals from Roberto Soldado and Adil Rami saw the three points go the Spaniards.
Chelsea still sit on top of the pool and are two points ahead of Leverkusen, three ahead of Valencia. The Stamford Bridge outfit still have to entertain the La Liga team, and travel to the BayArena in their next fixture in late November.
By Gareth McKnight