The rain was torrential throughout, but Pompey got off lightly as Newcastle won the all-Premiership encounter with a first ever United goal for Giuseppe Rossi and a double from Nobby Solano.
After six months on the sidelines, Kieron Dyer returned to the first-team squad with a place on the bench alongside Spanish misfit Albert Luque.
The pairing of Titus Bramble and Craig Moore were back in the heart of the defence with Steven Taylor switching to right-back and Celestine Babyaro returning to the left-back berth after missing the last six games.
Glenn Roeder rang the changes and Scott Parker was rested along with Damien Duff and Peter Ramage - the latter two named on the bench - while the on-loan Rossi was handed his first start in United colours.
Pompey also made changes and Harry Redknapp included the former United trio of Andy O'Brien and striking colleagues Andy Cole and Lomana LuaLua.
With great difficulty passing the ball, chances were at a premium, though Niko Kranjcar caused a problem when his long-range shot skidded off the surface and Steve Harper was unable to hold on as the ball squirmed behind for a corner.
United's first effort came on 26 minutes when Solano's free-kick from 20 yards in the centre of goal, hit a defender and looped into the arms of David James right under the bar.
A long ball from Solano in the 35th minute was missed by Linvoy Primus and Obafemi Martins broke on the right and spotting James off his line went for goal only to see the ball land in the netting on top of the goal.
Seconds later and LuaLua was put in the clear, but a woeful first touch saw him over-hit the ball and Harper was able to intervene.
James Milner then showed good skills to break into the box, but his shot was easily dealt with by James.
Both sides made a change at the interval, Duff replacing Martins and Pompey sending on Ognjen Koroman for David Thompson.
And within three minutes United had stormed in front through Rossi with the most clinical of finishes. A Solano corner was cleared as far as Babayaro to Duff, who picked out Rossi, who back-to-goal turned to beat James low to his left.
It was 2-0 after 54 minutes with Duff supplying the ammunition for Solano to score with a stooping back-post header for his first goal of the season.
Rossi then almost got a second when he was played in by Milner only for James to make an excellent black.
Dyer then made his long awaited return on the hour mark for Nicky Butt. Two minutes later from a Duff corner Bramble - who was outstanding - had a header blocked on the line by James and then a Dyer weaving run ended with him coming inches away from a dream return.
Then with the match heading into time added on, United struck for a third time when Solano put away his second of the night following an excellent Milner run.