A disappointing night on the south coast for Roberto Martinez's men, sunk by a Aruna Dindane hat-trick, and a Portsmouth side out with a point to prove.
In fairness Latics were second best too often and couldn't gain possession in the vital areas that they have been doing so well in recently.
Credit must go to Paul Hart's men who worked hard for their three points and the combined efforts of Frederic Piquionne, Hassan Yebda and Dindane were often too much to contend with.
Latics tried to get themselves going, but found it hard to work-out a link between midfield and attack, and when the man from the Ivory Coast, Dindane, put his side ahead, there was no looking back.
There was a suspicion of a foul on Scott Sinclair in the build-up, but the striker's finish was cool, and gave his side a deserved lead.
Hopes to re-group at half-time were dealt a blow when Piquionne doubled the lead seconds before the referee blew his whistle, slotting the ball through Chris Kirkland's legs in another display of fine finishing.
Re-emerging to the tune of 'Rocky' couldn't inspire to turn things round, and although there were valiant efforts from Charles N'Zogbia and Scott Sinclair, Portsmouth's responded to the threats well.
And so Dindane rounded things off, finishing into an open net, from Kanu's cross and converting a late penalty after Emmerson Boyce had fouled within the area.
Not the performance the gaffer was looking for at Fratton Park, and there will be plenty of work to do ahead of Fulham's arrival at the DW Stadium next Sunday.
