Jamal Lowe's first-half goal gave dogged Pompey a 1-0 opening-day win over Luton.
But Kenny Jackett’s side had to weather intense pressure from the newly-promoted visitors to get their first three points of the season.
Luton hit the woodwork twice and had a number of chances as they dominated territory.
Pompey were stoic, if lacking in attacking inventiveness, for much of the afternoon.
But that won't bother Jackett who has been determined for his side to show defensive resolve this term,
Pompey took the lead in the 16th minute, with Lowe getting the first goal of the campaign.
It was Ronan Curtis who took advantage of Alan Sheehan's slip and cut the ball back for Lowe to apply the finish from eight yards.
From there, it was the visitors who had the better of the chances.
Nathan Thompson made an important saving header to deny James Collins a goal in the 25th minute.
Then Pelly Ruddock fired a 20-yarder a whisker wid,e before Jorge Grant's free-kick from the right came back off the woodwork.
Dan Potts then headed wide for the visitors as the half came to a finish.
Curtis fashioned the first chance after the restart as Marek Stech kept out his drive in the 51st minute.
Then Collins' drive came off the underside of the bar before Craig MacGillivray kept out Harry Cornick's drive as Pompey remained entrenched in their half.
Pompey were riding their luck under the Luton pressure but continued to stand firm with some dogged defending.
MacGillivray earned applause from the home crowd as he dived full length to keeper out Alan Sheehan's free-kick with six minutes left.
And Jackett's side stood firm through four minutes of stoppage time to pick up the win.