Goals from Frank Lampard and Arjen Robben sealed a less than convincing win for the champions, who struggled to match the intensity and drama of their midweek defeat at the hands of Barcelona in the Champions League.
Players and supporters alike acted lethargic and struggled to motivate themselves for long periods.
But Jose Mourinho attempted to shake his charges out of it by replacing left-back Asier del Horno on 30 minutes.
The Spaniard lasted only 36 minutes of that titanic Champions League tie and from the first whistle Mourinho was on his case.
The confidence of the player must be at rock bottom and seeing left-winger Damien Duff replace him will have done him no good at all.
But had either of captain John Terry's headers gone in it might have been a different story.
Terry's first, after four minutes sailed over the bar. The second, on 32 minutes, was a diving header from six yards out which was well saved by goalkeeper Dean Kiely.
In fact Kiely was the pick of the bunch for relegation-haunted Pompey.
On 18 minutes the former Charlton stopper did well to parry away a Shaun Wright-Phillips low, right-footed drive.
Then five minutes before the break he was on hand to make a double save.
Ivory Coast striker Didier Drogba arrowed in a 20-yard free-kick which Kiely forced out into the path of Robert Huth, who headed back towards goal but straight into the gleeful arms of the keeper.
Pedro Mendes struck a speculative shot on 50 minutes for Portsmouth before Kiely again was called into action four minutes later to make another double save. This time a shot from Michael Essien was saved and the follow-up also from Frank Lampard.
Enough was enough for Mourinho, who, on 60 minutes, brought on Eidur Gudjohnsen and Claude Makelele for luckless Joe Cole and Wright- Phillips.
Chelsea finally made the decisive breakthrough five minutes later.
Gudjohnsen fed the ball out wide to Drogba. The striker, from the edge of the Portsmouth area, cut the ball along the area, Gudjohnsen dummied the ball fooling the defence and Lampard, lurking right on the edge of the box, slammed a trademark right-footer past Kiely.
Portsmouth tried to respond quickly and a fine chance went begging for Richard Hughes on 69 minutes when he failed to reach a fine, clipped byline ball from substitute Wayne Routledge.
Mendes tried another long-range effort on 71 minutes but, once again, it sailed high and wide of Petr Cech's goal.
Chelsea hit their second with 12 minutes remaining.
Lampard picked up a loose ball in midfield and fed the ball to Gudjohnsen.
The Icelandic striker took one touch to chip the ball over the heavy-legged Portsmouth defence into the path of in-running Robben.
The Dutch winger took one touch inside the box, before coolly slotting home a sidefooter past Kiely.