By Phil McNultyChief football writer at St Andrew's
Chelsea started the road to recovery after the sacking of Andre Villas-Boas by reaching the FA Cup quarter-finals with victory at Birmingham City.
Roberto di Matteo took control after being handed the job until the end of the season - but had to wait 45 minutes for Chelsea to move through the gears before finally finding the quality to see off their Championship opponents in this fifth-round replay.
Juan Mata enlivened a dour encounter with a scrambled finish just after the interval and Raul Meireles swiftly followed up with a spectacular second to confirm a sixth-round meeting with Leicester City at Stamford Bridge.
Mata also saw a penalty saved by Birmingham keeper Colin Doyle - as he did in the first game at Stamford Bridge - on a night when Chelsea's supporters delivered their own vociferous verdict on who they want to see replace Villas-Boas, sacked by owner Roman Abramovich on Sunday after only nine months in charge.
The name of former Chelsea manager Jose Mourinho was chanted within seconds, along with support for Abramovich, but there was a chorus of abuse and disapproval at the prospect of former Liverpool manager Rafael Benitez emerging as a potential contender to succeed Villas-Boas.
At the final whistle Chelsea were able to see a shaft of light at the end of a dark tunnel as an ultimately comfortable victory ensured they moved a step closer to Wembley.
Chelsea captain John Terry was fit well ahead of schedule following knee surgery to take his place on the substitutes' bench, where he was joined by Didier Drogba and Frank Lampard.
Di Matteo called for Chelsea to show unity and passion at the start of yet another new era at the club and Mata almost gave the Italian the perfect start in the opening seconds when was denied by Birmingham keeper Doyle.
The giant figure of Nikola Zigic was leading Birmingham's attack and he was galvanised into action by anger when caught late by Chelsea defender David Luiz, sustaining a nasty gash near his eye.
He required lengthy treatment, returning as a man on a mission. The Serb picked up a yellow card for a reckless lunge at Gary Cahill then forced Chelsea keeper Petr Cech into a fine save as he headed Jordon Mutch's cross towards the top corner.
Fernando Torres had been involved in plenty of Chelsea's approach play but summed up his current plight on the stroke of half-time when he turned superbly on the edge of the area before sending his finish hopelessly wide.
Phil McNultyChief football writer, BBC Sport
There was an interesting sub-plot in the Chelsea game. Not only were the Chelsea fans chanting Jose Mourinho's name and singing that Roman Abramovich sacks who he wants, but there was a strength of feeling against Rafael Benitez, who has been linked with the vacancy. I'm sure Abramovich will be aware of that. There will need to be things that change if Mourinho returns to Chelsea. He will want total control over all matters including who is brought in and out of the club.
Chelsea started with greater purpose after the break and went ahead nine minutes after the restart. Birmingham failed to clear Ramires's cross and in the subsequent scramble Mata bundled in a finish Doyle touched but could not keep out.
Mata almost added a second minutes later when Branislav Ivanovic's cross touched off Curtis Davies, a deflection which slightly wrong-footed the Spaniard, who could only poke his shot wide.
It was only delaying the inevitable as Chelsea finally exerted their authority and Meireles sealed their place in the last eight in spectacular style on the hour. The Portuguese, signed by Villas-Boas, met Ramires's touch with a crisp strike from 20 yards that was still rising as it hit the roof of the net.
Meireles's celebrations were subdued, perhaps out of respect to his fellow countryman Villas-Boas, in sharp contrast to Di Matteo and his cohorts on the Chelsea bench.
Birmingham began to flag, understandably given the depleted nature of their side, and Chelsea had the opportunity to add a third after 69 minutes when Torres was hauled down by Guirane N'Daw.
Chelsea's fans chanted for Torres to take the spot-kick - as did the Birmingham supporters who mocked the struggling striker throughout - but Mata stepped forward and saw his effort blocked by Doyle.
Substitute Daniel Sturridge then wasted a chance before Mutch squandered an opportunity to give Birmingham hope, lifting a wayward finish over the top from Chris Burke's excellent pass.
Birmingham had been a credit to manager Chris Hughton, battling to the end despite the cause being lost, with Marlon King forcing Cech to punch his volley to safety.
It was the final moment of anxiety as Chelsea survived in comfort to allow Di Matteo to start his time in charge with victory and another step towards Wembley.
Full Time The referee blows his whistle to end the game.
Morgaro Gomis sends in a cross, David Luiz makes a clearance.
Marlon King challenges David Luiz unfairly and gives away a free kick. Free kick taken by Petr Cech.
Substitution Michael Essien is brought on as a substitute for Juan Mata.
Wade Elliott produces a cross, save by Petr Cech.
Short corner taken by Jordon Mutch from the right by-line.
Marlon King takes a shot. Save by Petr Cech.
Nikola Zigic is flagged offside by the assistant referee. Free kick taken by Petr Cech.
Corner taken right-footed by Jordon Mutch, clearance made by Mikel.
The ball is swung over by Wade Elliott, clearance by Gary Cahill.
Raul Meireles challenges Nathan Redmond unfairly and gives away a free kick. Free kick crossed by Jordon Mutch, David Luiz manages to make a clearance.
Centre by Nathan Redmond, Gary Cahill makes a clearance.
Corner taken by Jordon Mutch, Juan Mata makes a clearance.
Inswinging corner taken right-footed by Jordon Mutch from the left by-line, clearance made by Frank Lampard.
Shot on goal by Jordon Mutch from inside the box goes harmlessly over the target.
Free kick awarded for an unfair challenge on David Luiz by Marlon King. David Luiz takes the free kick.
Jordon Mutch takes a outswinging corner from the right by-line to the near post, clearance made by Fernando Torres.
Gary Cahill challenges Jordon Mutch unfairly and gives away a free kick. The free kick is delivered right-footed by Jordon Mutch from left wing, save made by Petr Cech.
Substitution Ramires leaves the field to be replaced by Frank Lampard.
Shot by Nathan Redmond from just outside the area goes over the net.
Outswinging corner taken from the right by-line by Jordon Mutch, clearance by Branislav Ivanovic.
The ball is swung over by Nathan Redmond, Petr Cech makes a save.
The official flags Fernando Torres offside. Pablo Ibanez restarts play with the free kick.
Substitution Marlon King comes on in place of Guirane N'Daw.
Penalty taken by Juan Mata is saved by Colin Doyle. Birmingham 0-2 Chelsea.
Guirane N'Daw challenges Fernando Torres unfairly and gives away a Penalty.
Daniel Sturridge takes a shot. Save made by Colin Doyle.
Corner taken left-footed by Juan Mata to the near post, Curtis Davies makes a clearance.
Foul by Guirane N'Daw on Ramires, free kick awarded. The free kick is swung in left-footed by Juan Mata.
Shot by Juan Mata from just outside the area goes over the net.
Free kick awarded for a foul by Wade Elliott on Branislav Ivanovic. Direct free kick taken by Branislav Ivanovic.
Jonathan Spector takes the direct free kick.
Booking Fernando Torres is cautioned by the ref for unsporting behaviour.
Jonathan Spector fouled by Fernando Torres, the ref awards a free kick.
The assist for the goal came from Ramires.
59:44 Goal scored
Goal! - Raul Meireles - Birmingham 0 - 2 Chelsea Goal scored by Raul Meireles from just outside the penalty area to the top right corner of the goal. Birmingham 0-2 Chelsea.
Juan Mata takes the direct free kick.
Substitution Daniel Sturridge comes on in place of Salomon Kalou.
Substitution Chris Burke replaces Adam Rooney.
Foul by Adam Rooney on Juan Mata, free kick awarded.
Header from close in by Juan Mata misses to the left of the goal.
Outswinging corner taken by Jordon Mutch from the right by-line, clearance made by Branislav Ivanovic.
53:57 Goal scored
Goal! - Juan Mata - Birmingham 0 - 1 Chelsea Juan Mata grabs a goal from inside the six-yard box to the bottom left corner of the goal. Birmingham 0-1 Chelsea.
Branislav Ivanovic challenges Guirane N'Daw unfairly and gives away a free kick. Direct free kick taken by Colin Doyle.
David Luiz challenges Nikola Zigic unfairly and gives away a free kick. Jonathan Spector takes the free kick.
Outswinging corner taken right-footed by Jordon Mutch from the right by-line, save by Petr Cech.
The second half has started.
45:00 +2:03 Half time
Half Time The ref blows to signal half-time.
Fernando Torres concedes a free kick for a foul on Jordon Mutch. Colin Doyle takes the free kick.
Effort from the edge of the area by Fernando Torres goes wide of the right-hand upright.
Corner from right by-line taken by Juan Mata.
Ramires concedes a free kick for a foul on Curtis Davies. Curtis Davies takes the free kick.
Juan Mata takes a shot. Colin Doyle makes a save.
Corner taken by Juan Mata from the right by-line played to the near post.
Inswinging corner taken by Jordon Mutch.
Jordon Mutch produces a cross, Nikola Zigic takes a shot. Save by Petr Cech.
Jonathan Spector sends in a cross, clearance made by Raul Meireles.
Ryan Bertrand produces a cross, save by Colin Doyle.
The ball is sent over by Juan Mata, Guirane N'Daw manages to make a clearance.
Inswinging corner taken from the right by-line by Juan Mata, Gary Cahill has a headed effort at goal from close range which goes wide of the left-hand upright.
Gary Cahill takes a shot. Pablo Ibanez gets a block in.
Ramires produces a cross.
The offside flag is raised against Ramires. Colin Doyle takes the indirect free kick.
Direct free kick taken by Petr Cech.
Booking Nikola Zigic goes into the book.
Nikola Zigic gives away a free kick for an unfair challenge on Gary Cahill.
Free kick awarded for an unfair challenge on Jonathan Spector by Juan Mata. Centre by Jordon Mutch, Adam Rooney has a headed effort at goal from deep inside the area missing to the right of the target.
Wade Elliott takes a shot. Save made by Petr Cech.
Free kick awarded for a foul by Ramires on Morgaro Gomis. Guirane N'Daw restarts play with the free kick.
Fernando Torres sends in a cross, clearance by Guirane N'Daw.
The ball is delivered by Salomon Kalou.
Jonathan Spector takes a shot. Save by Petr Cech.
The referee blows for offside against Juan Mata. Indirect free kick taken by Colin Doyle.
Adam Rooney gives away a free kick for an unfair challenge on Ryan Bertrand. Free kick taken by David Luiz.
Effort on goal by Ramires from inside the box misses to the right of the target.
The ball is delivered by Salomon Kalou, Guirane N'Daw makes a clearance.
The official flags Adam Rooney offside. Indirect free kick taken by Petr Cech.
Jordon Mutch delivers the ball, Branislav Ivanovic manages to make a clearance.
Juan Mata is caught offside. Free kick taken by Curtis Davies.
The offside flag is raised against Fernando Torres. Colin Doyle takes the direct free kick.
Corner taken by Jordon Mutch played to the near post.
Jordon Mutch fouled by Fernando Torres, the ref awards a free kick. Curtis Davies restarts play with the free kick.
Inswinging corner taken from the right by-line by Juan Mata.
Juan Mata takes a shot. Save by Colin Doyle.
Unfair challenge on Jordon Mutch by Salomon Kalou results in a free kick. Jordon Mutch restarts play with the free kick.
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