Craig Westcarr was the match-winner for Pompey at Oxford today.
The striker struck with 10 minutes left to keep up a flying start to the season for the Blues in the 1-0 win.
Pompey dug deep and were resolute as Michael Appleton’s side pushed for a leveller.
But Andy Awford’s side were rock solid at the back to earn the win and lift themselves to second in the table.
Joe Riley set the tone for the first half with a blazing free-kick from after two minutes - which Paul Jones superbly tipped wide.
Jones then immediately saved at point blank range from Calvin Morris.
Pompey should have been in front after 10 minutes when Nigel Atangana was clean through, but fired wide from six yards.
Atangana then almost headed into his own goal after 20 minutes, but Shorey cleared off the line.
There were chances coming at both ends, and Storey was put clear five minutes before the break, but fired at George Long.
Danny Hylton could have had an hat-trick from one attack when he had a shot saved by Jones, hit the post and then saw a further effort blocked.
And there were strong appeals for a penalty ignored on the half-time whistle as Hylton went down under the attentions of Craig Westcarr - but ref Darren Bond waved play on.
Hytlon had a header saved by Jones four minutes after the restart.
Then Jed Wallace - on for Holmes - reached the byline but saw his cross-shot deflected for a corner.
Pompey had a good period of pressure midway through the half, but couldn’t make a clear opening from their play.
That changed, though, with 10 minutes left with Westcarr’s match-changing intervention.
Then Jones made a crucial stop to deny Junior Brown a leveller moments later.
That proved a key late moment before Brown headed over at the death - and Pompey held out for the win.