Pompey’s lead at the top of League One was cut to four points after being held to a 1-1 draw at Barnsley.
Gareth Evans was on target for Kenny Jackett’s men two minutes before half-time, before Cauley Woodrow equalised for the Tykes after the interval.
Nevertheless, the Blues’ unbeaten away record this season stretched to 14 matches in difficult conditions at Oakwell.
Barnsley had the better of the play in the opening period, with Craig MacGillivray forced to make a number of decent saves.
Kieffer Moore, Woodrow and George Moncur all tried their luck from long rang – all of which were thwarted by the Pompey keeper.
In truth, the Blues were second best – yet took the lead against the run of play two minutes before half-time.
Alex Mowatt’s scuffed clearance fell kindly for Evans on the edge of the box and his clinical left-foot finish found the corner of the net.
The rain and wind worsened in the second half and the Tykes grabbed an equaliser on 62 minutes.
Brad Potts’ inviting delivery was met by Woodrow at the near post and he instinctively stabbed his shot beyond MacGillivray.
Oli Hawkins threatened to restore the visitors’ lead five minutes later but his angled right-foot effort was kept out by home keeper Adam Davies.
Jackett replaced Ronan Curtis with Anton Walkes in the 75th minute – clearly happy to settle for a point.
But Barnsley almost grabbed a 90th-minute winner but Moore’s shot on the swivel just missed the far post.
With Luton winning at Coventry, the Blues are now four points clear at the summit of the division.
Nevertheless, a point against their promotion rivals should be deemed a good result, with Pompey top at Christmas.