Brett Pitman was Pompey's snowy sniper as they grabbed a 2-0 win in blizzard conditions at Oldham
Two first-half goals from the Blues' fit-again skipper ensured Pompey delivered their third win of the year.
The game will be remembered for the conditions it was played in, with heavy snow placing the march in doubt after the break.
But ref Seb Stockbridge allowed the clash to be played out and Kenny Jackett's men grabbed their first clean sheet in 16 games.
Jackett sprung a pre-match surprise as Jack Whatmough replaced Christian Burgess, with Pitman also coming into the starting XI.
Brandon Haunstrup was almost punished in the 20th minute when he lost the ball and it was fed to Blues old boy Eoin Doyle, who poked his shot at Luke McGee.
Wilfried Moimbe was then required to clear off the line from Whatmough's header after Dion Donohue's corner.
The opener came in the 29th minute with a fine headed finish from Pitman, as he rose early to glance Connor Ronan's cross past keeper Johny Placide.
Pitman's second came three minutes before the break when Placide lost the ball to the striker, who managed to guide it through the keeper at the second attempt.
The second half saw the snowy conditions worsen to the point the game was placed in doubt.
The official stopped play after the 63rd minute and was involved in lengthy conditions with officials and staff of both sides.
After the groundsman eventually cleared the pitch markings, the game continued after a nine-minute delay.
McGee superbly tipped over Doyle's swivel-shot from 10 yards with 13 minutes remaining.
Kal Naismith could've have settled it with five minutes left as Pitman squared to the Scot, but he allowed Placide to smother the ball a few yards out.
There was a whopping 11 minutes of stoppage-time added at the end of the game.
Jamal Lowe fired a drive off the post from a tight angle in that time, but Pompey held on for a hard-earned three points.