Didier Drogba scored twice to take his tally to 24 goals in 27 league matches as Chelsea bounced back from the disappointment of dropping points in a draw with Blackburn last weekend.
Florent Malouda also scored twice at Fratton Park with England midfielder Frank Lampard adding a fifth goal late on
Florent Malouda of Chelsea celebrates his second goal with Didier Drogba, who also scored twice against Manchester United.
(Phil Cole/Getty Images)
Elsewhere, Australia's Tim Cahill scored for Everton in a 2-0 victory over Manchester City as the Merseysiders became the first away side to win in the league at Eastlands this term - a result that dented their hosts' hopes of Champions League qualification.
Meanwhile Aston Villa and Sunderland drew 1-1 and Blackburn defeated Birmingham 2-1.
On a day when cash-strapped Pompey, hit last week with a nine-point penalty for entering administration, were given permission to sell players outside of the transfer window, one of their few prize assets helped gift Chelsea the lead.
Chelsea went ahead in the 32nd minute thanks to the latest howler to befall Portsmouth goalkeeper David James.
Nicknamed 'Calamity' for a series of high-profile mistakes, the England international wasn't helped by a bad bounce as he missed completely with an attempted kick in a bid to clear Deco's header.
James's error let in Drogba, who shot into the empty net.
Malouda, booked earlier for elbowing Ricardo Rocha, doubled Chelsea's lead early in the second half with a fierce shot.
France winger Malouda then put the result beyond doubt on the hour mark when, after James palmed out Lampard's shot, he followed up to score.
And there was still time for Ivory Coast striker Drogba to get his second goal, in the 77th minute, when he ran onto Jon Obi Mikel's pass, shrugged off Steve Finnan and scored at the near post.
Manchester City kicked-off fifth in the table.
With only the leading quartet at the end of the season guaranteed Champions League football next term, Roberto Mancini's men were looking to leapfrog Tottenham Hotspur into fourth place with their rivals involved in an FA Cup quarter-final replay against Fulham that Spurs won 3-1 on Wednesday.
But it was the visitors who took the lead when Cahill headed in a cross from Leighton Baines's through a crowd of players in the 33rd minute.
Cahill's clever dummy then set up Spanish midfielder Mikel Arteta, who sealed victory five minutes from time before Mancini and Everton counterpart David Moyes were both sent to the stands after a touchline row.
Sunderland went ahead at Villa Park when Frazier Campbell latched onto Kieran Richardson's defence-splitting pass in the 22nd minute.
However, eight minutes later Villa, still in the hunt for fourth place, were level after in-form Norway striker John Carew headed in England international winger Ashley Young's fine cross.
At Ewood Park, David Dunn put Blackburn ahead against his former club in the fifth minute with a fine strike from the edge of the penalty area.
Scotland international James McFadden equalised for Birmingham in the 55th minute with a perfectly-placed free-kick, but Dunn grabbed the winner in the 67th minute, heading home El-Hadji Diouf's corner.