Cesar Peixoto's side missed a chance to close the gap on the Championship's pace-setters after failing to turn their dominance into more goals.
Four days after Tawanda Chirewa came off the bench to score Wolves' winner at Burnley, substitute Jordan James' 62nd-minute strike rewarded Peixoto for another inspired move.
But Portsmouth right-back Terry Devlin popped up with a fine finish in the 86th minute to leave Wolves frustrated.
The scoreline was harsh on Wolves as Chirewa hit the bar and was denied another goal, while Mateus Mane and Fer Lopez missed chances in a dominant second-half performance.
Wolves, relegated from the Premier League last season, sit in seventh place in the second-tier table, four points adrift of second-placed West Ham in the race for automatic promotion.