And, the Eagles were only prevented from grabbing a shock victory by an outstanding save from Pompey keeper Shaka Hislop.
In clinging mud, Portsmouth struggled to find any rhythm or the sort of form which has made then runaway leaders during the first half of the season.
However it was the home side who took the lead in the 27th minute.
Matt Taylor seized on a poor control by Tommy Black to run 60 yards before setting up an easy chance at the far post for Paul Merson to score his seventh goal of the campaign.
But Palace hit back almost immediately when Black made up for his mistake by floating in a centre from the right.
The Portsmouth defence only cleared as far as Julian Gray, who scored with a fierce left foot shot from 15 yards.
Hayden Mullins sliced wide from 12 yards late in the first half and, then as action swung to the other end, Svetoslav Todorov hit the bar.
Portsmouth rattled the woodwork again in the 64th minute but it was Palace who came the closest to taking all three points ten minutes later when Hislop brilliantly dived to his right to turn away a goalbound effort from Adi Akinbiyi.