Chelsea dropped their first points of the season in a draw at Aston Villa.
Villa started well and Petr Cech tipped a Thomas Hitzelsperger free-kick around the post before Chelsea replied, Didier Drogba's curler slamming off the bar.
Juan Pablo Angel volleyed over before Chelsea stepped up a gear, Joe Cole forcing Thomas Sorensen to save well and seeing another shot blocked.
Darius Vassell dragged a late shot wide before Drogba was booked for an alleged dive when he may have won a penalty.
Gareth Barry and Hitzelsperger were at the forefront of Villa's attacking intent, the German forcing a fine save from Cech with a 30-yard free-kick early on.
Chelsea replied as Drogba controlled a long pass and lashed his right-foot shot across the face of goal, but it was Villa doing the majority of the pressing.
Nolberto Solano slammed a 25-yard effort wide before Hitzelsperger dragged another shot off target, this time with his weaker right foot.
Chelsea had conceded just one goal in their previous four league games, and their defensive fortitude was managing to keep Villa at bay.
At the other end Mateja Kezman used his pace to create space down the right-hand side, but his fierce cross-shot was deflected wide by Cole.
Moments later Drogba went within inches of an opener, his sublime 20-yard curler after a neat build-up crashing back off Sorensen's crossbar with the Dane well-beaten.
A relatively quiet spell - with Villa again probing but failing to find a way through - was interrupted by a lovely run and cross by Frank Lampard, but Kezman could only head over.
Solano's right-wing cross then invited Angel to have a go, the Colombian volleying acrobatically over from 12 yards.
Chelsea knew the three points were there to be won and they soon had Villa under huge pressure after the break.
First Lampard drove wide of the target before Cole's impressive right-foot effort was tipped around the post by Sorensen.
Soon after Cole's goalbound shot was blocked by Gavin McCann while Ricardo Carvalho missed the target after Villa failed to deal with another cross into their box.
Mourinho made a surprising double change on the hour mark, taking off Kezman and the excellent Cole and bringing on Eidur Gudjohnsen and Adrian Mutu, a move that seemed to knock Chelsea off their attacking stride.
With 15 minutes left Villa put a fabulous move together, Lee Hendrie - on for Solano - brilliantly dummied a pass into the Chelsea box only for Vassell to drag a shot wide from eight yards.
But the hosts could count themselves fortunate when Ulises de la Cruz seemed to foul Drogba in the area, only for referee Rob Styles to show the striker a yellow card for a dive.
John Terry had the final opportunity, his header from a Lampard corner producing a comfortable diving save from Sorensen in stoppage time.
Aston Villa: Sorensen, De la Cruz, Delaney, Mellberg, Samuel, Solano (Hendrie 57), McCann, Hitzlsperger, Barry, Vassell (Whittingham 90), Angel (Moore 67). Subs Not Used: Postma, Davis.
Chelsea: Cech, Paulo Ferreira, Terry, Ricardo Carvalho, Babayaro, Tiago (Smertin 66), Makelele, Lampard, Cole (Mutu 61), Kezman (Gudjohnsen 61), Drogba. Subs Not Used: Pidgeley, Gallas.
Ref: R Styles (Hampshire).