A first-half own goal by Brynjar Gunnarsson after 10 minutes from a corner from Pedro Mendes sent Pompey one-nil up.
Nwankwo Kanu headed in a second from the six yard box after the half-time break.
Mendes volleyed a third from the edge of the box, with Reading’s scoring a late stabbed finish from Kevin Doyle with six minutes to go.
Both teams were looking to bounce back from midweek Carling Cup defeats and it was the Pompey who dominated from for large parts of the match.
Pompey missed several good chances in the first half, with Benjani Mwaruwari guilty of missing the ball completely on the six yard line and firing wide when he only had to shoot straight.
Reading did get one back and in the final 10 minutes improved. Doyle pulled the ball back which resulted in after a goalmouth scramble following a mistake from David James.
Manager Rating
Harry on Kanu:
“He has been fantastic. Seven goals already is amazing. And he could easily have been given our first one today as well.
“He keeps on heading the ball in and before I brought him here I didn’t think he could head it at all.
“We decided to go at them from the first whistle and it paid off with some great football.”
Opponent Rating
Reading Manager On Pompey:
“We were up against a strong outfit, well-marshalled at the back, a keeper playing at the top of his game and a powerful, competitive midfield.
“And there was Kanu’s finishing. We got back into it then but it was too late.
“If we keep putting our best side out I can guarantee we will be all right. Pompey will definitely be looking up this season rather than down.”