While so many big clubs have fallen by the wayside in this season’s competition, Chelsea have reached the quarter-finals with little trouble.
Chelsea 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.
“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.
“We are fortunate to have a squad of players who we can change. We took quality out and put quality in.”
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 (third division) Southampton in their first south-coast derby for five years.
Pompey though went ahead after 66 minutes with a neat curler by substitute Quincy Owusu-Abeyie, only for Rickie Lambert to nod the equaliser with his 25th goal of the season.
Aruna Dindane restored Portsmouth’s lead before Nadir Belhadj and Jamie O’Hara completed a rare win.