After a season of shocks, the upsets dried up in the fifth round as Birmingham City came from behind to win 2-1 at Championship side Derby County with a last-minute goal by Liam Ridgewell while Manchester City and Stoke City drew 1-1.
Reading, conquerors of Liverpool and Burnley in previous rounds, drew 2-2 at home to West Bromwich Albion after taking the lead after nine seconds of the all-Championship tie.
Saturday's game at Stamford Bridge was preceded by a minute's applause in honour of former Chelsea and Yugoslavia goalkeeper Petar Borota after he died at the age of 57.
His former team were ahead after two minutes with a Didier Drogba goal but with captain John Terry away on special leave, their vulnerability to the cross was exposed again after 34 minutes when Michael Chopra headed the equaliser.
It was one-way traffic in the second half though as Michael Ballack, Daniel Sturridge and Salomon Kalou sent the Londoners through without further alarms.
CITY GIFT
"They played exceptionally well in the first half but fortunately we upped the tempo in the second and in the end it was easy for us," Chelsea assistant manager Ray Wilkins told reporters.
Manchester City were gifted the lead when Ryan Shawcross made a complete mess of an 11th-minute goal-line clearance and allowed Shaun Wright-Phillips to tap the ball into an empty net.
However, as so often this season, Roberto Mancini's team failed to push on and Stoke levelled after 57 minutes when Ricardo Fuller headed in a Rory Delap long throw.
Portsmouth, bottom of the Premier League and fighting for their existence in the High Court, were second best for a long time against League One Southampton in their first south-coast derby for five years.
Pompey though went ahead after 66 minutes through substitute Quincy Owusu-Abeyie.
Rickie Lambert equalised but Aruna Dindane, Nadir Belhadj and Jamie O'Hara completed a rare win for the visitors.
Jimmy Kebe's goal for Reading was timed by his own club at nine seconds. Others clocked it at seven seconds, either way it beat the previous quickest in the competition proper of 13 seconds by Aston Villa's George Edwards against Manchester United in 1948.
West Brom equalised through Robert Koren and again through Joe Mattock after Reading had led again through Simon Church.
Both teams had a player sent off in the second half.
