Manchester City manager Kevin Keegan has vowed to spend big in this month's transfer window to put a stop to his side's free fall down the Premiership table.
This 4-2 defeat means that City have now gone 14 games without a win and stand only three points off the third allotted relegation spot.
Keegan said: "Today's result was very hard to take but we need to get real with what's going on at the club.
"After our good start to the season people were starting to talk about Europe, but since then we've got into a sticky situation and we are now talking about relegation.
"I am aware of this and I believe that we have been involved in the relegation battle over the last four weeks and maybe we need a couple of new faces around the place so we can dig ourselves out of it." Keegan saw his side squander a first-half lead as they conceded three second-half goals to a Portsmouth side who are now, themselves, out of the bottom three.
City's afternoon didn't start well and they were dealt a blow on 12 minutes when goalkeeper David Seaman went off injured after an innocuous collision with Portsmouth striker Yakubu Ayegbeni.
Things didn't get better on the pitch when on 19 minutes Patrick Berger's in-swinging free-kick was met by Pompey defender Dejan Stefanovic who headed his second goal of the season.
Portsmouth's lead only lasted 90 seconds before City' Antoine Sibierski crossed from the left and Trevor Sinclair's headed centre found Nicolas Anelka who volleyed home an instant equaliser.
The visitors hit the woodwork three times in the first half, twice through Robbie Fowler with a sweet half-volley and a header that hit the top of the upright.
On 40 minutes the lively Sibierski saw his free-kick come back off the crossbar just seconds after Teddy Sheringham threatened to give the home side the lead, only to mis-kick.
But right on the stroke of half time Anelka was again involved as he flicked on Joey Barton's cross to allow Sibierski to thunder home from 10 yards.
Portsmouth came out in determined fashion in the second period and the impressive Ayegbeni struck an equaliser after 52 minutes after being played through by strike partner Sheringham.
And only six minutes later the home side took the lead when another in-swinging free-kick from Berger found Sheringham six yards out and he made no mistake with a trademark header, to score his first goal since October.
City searched in vain for an equaliser and in the 61st minute Fowler's left-foot shot from distance troubled the home keeper Shaka Hislop who had to palm it away to safety.
But, it was to be Ayegbeni's afternoon in his last game before he goes off for African Cup of Nations duty with Nigeria, as he added his second and Portsmouth's fourth to seal the win.
Midfielder Richard Hughes' long ball through the centre and Ayegbeni latched onto it, outpacing Sylvain Distin before slotting past stand-in keeper Kevin Stuhr-Ellegaard.
The Nigerian has vowed to make up for lost time when he returns from Tunisia in a month's time in a bid to secure Portsmouth's Premiership status.
"I have now got to go away for three to four weeks which is hard for the team, but I will do everything I can when I come back to help us stay in the Premier League," he said.
"We need to stay up, we can't afford to be relegated and we feel as a team we are good enough to be playing in the Premier League every week."