Pompey’s unbeaten home record came to a disappointing close with a 2-1 loss to Doncaster Rovers.
First-half goals from former Blues striker John Marquis and Andy Williams did the damage in front of a crowd of 16,950 at Fratton Park.
Carl Baker pulled one back before the interval for Paul Cook’s side.
The Blues huffed and puffed in the second half but could not find an equaliser.
There was a late charge as Pompey pushed bodies forward in search of a leveller, but it’s now two defeats on the bounce as Pompey drop to sixth in the table.
Pompey were left to rue a shoddy start with more defensive instability costing them dearly.
The opener arrived after seven minutes as a ball over the top caught Christian Burgess out position.
David Forde then charged from his box but Marquis skipped around him and fired into an empty net.
Cook’s side looked like they were recovering with half chances falling to Carl Baker and Conor Chaplin.
But they fell further behind after 34 minutes when another ball into the box wasn’t dealt with, and Williams nicked the ball past Forde as he swivelled from six yards.
Gareth Evans looked to have a decent appeal for a penalty three minutes later, but ref Darren Deadman judged it was a dive and booked the Pompey man.
Marko Marosi then produced a top-drawer save to keep out Baker’s 30 yarder as Pompey upped the ante.
Then Baker reduced the arrears three minutes before the break, as Joe Wright bizarrely cleared a ball heading out of play into the danger area and the Pompey man ripped it home from 10 yards out.
Marquis was the first to threaten eight minutes after the restart as he fired wide from the edge of the box.
Then Chaplin couldn’t direct his header into the unguarded net from Roberts’ cross after 63 minutes.
Burgess should have done better three minutes when he put a free header wide from a corner.
Lalkovic’s shot looked to be looping in after a deflection off Baker after 73 minutes but hit the top of the bar.
Then Main couldn’t force his shot home from a few yards out as Roberts’ ball found the former Doncaster man.
Doncaster looked to have the chance to settle the game as Williams broke clear with Forde off his line, but the keeper recovered to save as he pulled the trigger.
Roberts appeared to have equalised with nine minutes left when he met Bakers’ cross in the six-yard box, but Andy Butler cleared off the line with the Pompey bench believing it had gone in.
There was a late charge from Pompey as the home crowd willed them forward, but the goal never looked like coming after Roberts’ effort.