While a third successive 6-0 victory never looked on the cards in a comparatively low-key Blues display, the result was rarely in doubt aside from a moment midway through the second half when Whelan's superb effort bounced down off the underside of Petr Cech's bar.
In the replay, Benitez's deployment of Ba, Eden Hazard and Juan Mata up front proved key -- as did Petr Cech's superb one-handed save to deny Javier Hernandez's header to keep Chelsea ahead in the game.
Midfielder Frank Lampard said he and his team-mates have been taken aback by the speed of Cech's return.
BBC: Chelsea keeper Cech had surgery on his skull in October
Adam Barrett headed the hosts into a shock lead from a corner, while Alex Revell also stung Petr Cech's palms.
The Potters then went agonisingly close to a leveller when Whelan walloped a long-range strike against Cech's crossbar with the home side's keeper beaten.
The Baggies deserved to extend their advantage when Brunt poked Marek Cech's low centre just wide after a stunning one-touch move, but a second goal was soon forthcoming.
But Everton had other ideas and after they were awarded a free-kick on the edge of area, Baines stepped up to curl a delightful set-piece into Cech's top left-hand corner.
Cech's understudy Ross Turnbull suffered a traumatic start when he was forced to retrieve the ball from his net after only six minutes as Zewlakow slid home from Constantino Charalambides's pass.
The hosts, full of graft and bite, hit back immediately when Phil Neville lashed a low drive into Blues keeper Petr Cech's arms before Cahill and Marouane Fellaini had headed attempts on goal.
The Brazilian carelessly knocked into the legs of Dempsey to concede the penalty but was reprieved when the American blasted straight at Cech's tall frame and then acrobatically blazed the rebound high and wide.
Despite Cech's save in the 93rd minute to rescue a point, with leaders United and second-placed Arsenal both winning at the weekend, Carlo Ancelotti's team remained in fifth place and face a monumental task to retain their crown.
Hernandez struck first, looping a header over Petr Cech from Michael Carrick's floated pass.
Chelsea goalkeeper Petr Cech echoed his manager's thoughts over whether Manchester City can buy their way to glory.
"I am really happy to be part of this great club for another four years, " Cech told the club's official website.
Florent Malouda went close as Chelsea dominated before Kieron Dyer was denied by Peter Cech and Diego Tristan's flick was cleared off the line.
Wayne Rooney emerged from his first-half shell to bring a first save out of Petr Cech and tested Chelsea's back line with a couple of bursting runs.
But, on the pitch, his players kept their focus and Chelsea were lucky to escape again when Petr Cech missed Stewart Downing's cross and only a flick from Terry diverted the ball out of John Carew's path at the far post.
That was not Southend's only chance of the half and it took a superb point-blank save from Petr Cech to keep out Alex Revell's header on 40 minutes to keep the scores level.
But West Brom's defensive problems got worse on the half hour mark when Marek Cech was caught on the knee by John Pantsil's trailing leg and the Slovakian had to be replaced by Nicky Shorey at left-back.
West Ham had a chance to equalise when Kalou fouled Hireta Ilunga but Cech superbly saved Mark Noble's penalty.
The hosts went close on 51 minutes when Petr Cech kept out Warren Feeney's shot and Chris Brunt fired the rebound over.
And just after the break, Zamora should have punished Chelsea when he intercepted Ricardo Carvalho's backpass but Petr Cech made a fine save.
Their luck slowly began to change after the break, though, and finally turned courtesy of a horrible mistake by Czech Republic's highly experienced goalkeeper Cech.
El-Hadji Diouf equalized for the home side in the 70th minute when he rose above Paulo Ferreira to cleverly direct Michel Salgado's cross past Petr Cech.
Ricardo Carvalho needlessly fouled Larsson, and Ronaldinho's swerving free-kick glanced off Terry's head and flew over Cech.
Stoke took the lead at Stamford Bridge through Rory Delap's deft chip over Petr Cech after 60 minutes.
The hosts rarely threatened before Clint Dempsey was fouled by David Luiz in stoppage time, only for Cech to keep out the American's spot-kick.
City could easily have been ahead by a bigger margin at the break, as James Milner's shot in the 39th beat Cech but was inadvertently blocked by Aguero.
Liverpool captain Steven Gerrard shot straight at Cech after seven minutes, then Kuyt's poor control let him down after he was sent clear by Xabi Alonso, allowing the Chelsea keeper to make the clearance.
Chelsea stopper Cech reacted quickly to push David Rozehnal's wayward header round the post but the Czechs broke quickly from the resulting corner, only for Libor Sionko to hit a weak shot which was easily saved by Taylor.
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