Birmingham City 0 Chelsea 0: Mourinho's darkening demeanour putting pressure on Chelsea's players

What a peculiar situation Chelsea find themselves in. To be seven points clear in the Premiership with six games left is a luxury Jose Mourinho's predecessors dreamt of for 100 years.

But just as the champions' faltering momentum has led Manchester United to think the unthinkable, so this "stalemate kind of game", as Frank Lampard termed it, suggested that their manager's petulance under pressure is affecting his players.

In contrast with the antics of Steve Bruce and the Birmingham bench, Mourinho and his staff tended to sit, scowling and with arms folded, like sulking infants. When Chelsea were ruthlessly racking up the wins, the Portuguese would stroke his stubble and issue instructions. Then they ran into adversity, since when he has increasingly subjected his team to glares that would melt rock and critics to sulphuric put-downs.

While they remain odds on to retain the title, it was difficult to resist the feeling at St Andrew's that Chelsea's aura of invincibility has evaporated. The same fate befell Arsenal last season after their long unbeaten run ended at Old Trafford. The surprise with Mourinho's men is that it took no more than a defeat at Middlesbrough, admittedly followed by the Champions' League exit in Barcelona, to hint at a sense of turmoil.

The Special One compounded the impression when he protested, in the face of overwhelming evidence to the contrary, that Ricardo Carvalho had not interfered with play before Asier del Horno put the ball in the home net. The incident came midway through a second half in which Chelsea dominated possession after a mediocre first 45 minutes.

Mourinho's irritation, exacerbated by the sight of Hernan Crespo and Carvalho each spurning last-minute opportunities, was the sound of a normally urbane character parting company with reality. He accepted that Birmingham deserved a draw. Yet it was his over-cautious tactics at the start, when Chelsea had only Didier Drogba against a makeshift defence which featured two irregular full-backs, that allowed vulnerable opponents to establish a pattern of defiant resistance.

Lampard, along with John Terry and Claude Makelele, has usually provided a pragmatic counterweight to the flakier side of Chelsea personified by Drogba and Arjen Robben. Perhaps worryingly for Sven Goran Eriksson as the World Cup looms into focus, he currently appears heavy-legged. He has failed to score in five matches, his longest barren run this season, and never threatened to do so here.

The England midfielder followed Mourinho in acknowledging Birmingham's fighting spirit, which was light years removed from their 7-0 surrender to Liverpool. Bruce's patched-up side will escape the relegation zone for the first time in six months if they beat Bolton at home tomorrow, although it will be asking a lot for Damien Johnson and Nicky Butt to repeat the energy-sapping harrying and tackling that subdued Lampard and Makelele.

"We had to restore the attitude of being hard to beat," Bruce said. "Over the past 18 months we've tried to change that philosophy because you try to improve by getting in better players and trying to play more open, attractive football. We had to go back to basics and to do that I had to rely on players who have been with me a long time. I always know what I'm going to get off them and they gave everything they could."

Bruce spoke of creating a "siege mentality" (which, for a disciple of Sir Alex Ferguson, should be second nature); like Mourinho, he perceives himself to have been unfairly abused by sections of the press. Now, though, with Portsmouth on a roll, Birmingham actually have to win matches. The difference in the mind-set required to beat Bolton is different from that necessary to stifle Chelsea, especially for a team who have not scored from open play in more than nine hours of action.

Having had nine players unavailable for this game, Bruce hopes "big hitters" Chris Sutton, Muzzy Izzet and David Dunn will be fit for the run-in.

On Saturday, however, he was indebted to the journeyman pros, like Johnson and Olivier Tebily, who played "the game of his life" according to his manager. They found the fire in the belly that Birmingham need and Chelsea must summon if they are not to be caught by United.

Birmingham City (4-5-1): Maik Taylor; Tebily, Cunningham, Martin Taylor, Sadler; Pennant, Butt (Kilkenny, 87), Johnson, Clemence, Campbell (Forssell, 57); Heskey. Substitutes not used: Vaesen (gk), Latka, Lazaridis.

Chelsea (4-5-1): Cech; Ferreira, Carvalho, Terry, Del Horno (Crespo, 64); Robben, Gudjohnsen (Essien, 68), Makelele, Lampard, Duff (J Cole, 64); Drogba. Substitutes not used: Cudicini (gk), Huth.

Referee: D Gallagher (Oxfordshire).

Man of the match: Johnson.

Attendance: 26,364.