Kenny Jackett had an unhappy reunion with his old team as Rotherham picked up a 1-0 win.
A first-half goal from Jon Taylor did the damage on a frustrating afternoon in front of the Sky Sports cameras at Fratton Park.
Jackett ditched his wing-back formation at half-time as the Blues stuttered in the teeming rain.
Pompey were better after the break after a switch of system but the leveller wouldn’t come.
Jackett made four changes as new boys Oliver Hawkins and Stuart O’Keefe were given their bows. Damien McCrory and Matty Kennedy were on the bench.
And there was the boost of Matt Clarke being given his first start of the season after a groin injury he picked up in pre-season.
The only goal came nine minutes before the break as Taylor powered home from Blues old boy Ryan Williams defence-splitting pass.
Jamal Lowe and Clarke both failed to get decent headed chances on target for Pompey.
And Lowe saw a decent chance go wide just after the restart.
A goal line clearance from Darren Potter denied Hawkins a debut goal after 64 minutes
And Hawkins had a decent penalty shout turned as he took a boot in the head from Michael Ihiekwe.
Lowe couldn’t tap in Clarke’s cross at the back post as Pompey pushed for a leveller.
The goal didn’t look likely to come through six minutes of stoppage time to leave the Blues 16th in League One.