Moore's side have lost four of their last six matches to slip to seventh place, two points adrift of the play-offs.
Pompey striker David Connolly tapped in Yassin Moutaouakil's cross after 53 minutes to extend his side's unbeaten run to four games.
Moore said: "We're gutted that we're seventh in the league, but if someone had said we'd be there earlier in the season, we'd have snatched their hands off.
"We've got to make sure we at least get to the play-offs. It's going to be tight; it's going to be tough with four games to go. We need at least two wins out of them and we need to perform better than we did here.
"We're running out of games. We're out of the play-off spots, which is disappointing, but maybe that's the kick up the backside that'll drive us on. At this present time, I can't see where a goal is coming from.
"Earlier in the season we were getting the breaks, everything was going for us and it was brilliant. Now it's not and it's a difficult time. But let's pick ourselves up and get on with it."