Noel Hunt's first-half header was enough to earn the Royals a seventh consecutive win in a game of few chances, but the outlook appears bleak for Pompey.
The cash-strapped Hampshire side have now gone seven games without a win since entering administration for a second time in two years, during which time they have managed only two goals.
Reading boss Brian McDermott was forced into a single change from the side that beat Millwall at the weekend, with Shaun Cummings replacing Matthew Connolly after the defender suffered an ankle injury.
Michael Appleton, who reiterated his belief his side could escape relegation after a 3-1 defeat against Middlesbrough on Saturday, brought in Aaron Mokoena and fit-again Luke Varney for Marko Futacs and Tal Ben Haim. While Futacs was on the bench, Ben Haim - Pompey's highest earner on a reported £36,000 per week - did not travel.
Varney produced a lively cameo from the bench on Saturday and he showed what goal-shy Pompey have been missing for three months with some sublime skill to get to the byline early on, only for Kaspars Gorkss to head away his cross with Joel Ward lurking.
Reading began to dominate from then on, though, with Jobi McAnuff tormenting former Royal Greg Halford on the right wing.
When Halford fouled the former Crystal Palace man, Ian Harte's free-kick was headed narrowly over by Alex Pearce, and minutes later McAnuff was obstructed again - this time by Hayden Mullins - and Harte's centre was nodded wide by Gorkss.
Pompey produced some attractive football, but not surprisingly a side that now have only one goal from open play in their last seven matches lacked a cutting edge. The impressive Scott Allan embarked on a mazy run, but Gorkss was alert to snuff out the danger and prevent him playing in Ward.
Jason Roberts looked a threat whenever Reading attacked, and after 23 minutes he skinned Jason Pearce on the touchline before firing in a dangerous cross that Ricardo Rocha had to be alert to put behind for a corner.
From the resulting set-play the ball found its way back to veteran Harte, who played Roberts in down the right. The former Blackburn man beat Ward, and his superb centre was powerfully headed past Stephen Henderson by Hunt.
Six minutes before the interval McAnuff's dangerous centre found Hal Robson-Kanu unmarked at the back post, but he headed tamely at Henderson.
There was more purpose to Portsmouth's play after the interval - David Norris played in Ward down the left, but his cross was overhit and went behind for a goal kick.
Allan went on another good run after 61 minutes, beating two men after collecting Mullins' pass - only to see his shot blocked. The ball was then worked back to Varney, but his effort was also charged down.
The game petered out after that, Allan trying his luck with speculative efforts from 40 and 30 yards which failed to test Adam Federici, while at the other end McAnuff beat Ward with ease, but Hunt could only rifle his low cross into the side-netting.
