Ryan Taylor rued his missed opportunity as Pompey slipped to a first league defeat of the season.
Newport County shocked the Blues on Saturday by claiming a 1-0 victory through Andy Sandell’s 84th-minute free-kick.
It was a flat display from Andy Awford’s men who, despite plenty of possession, struggled to muster a shot on goal.
Taylor had one of the best chances but could only fire Jed Wallace’s fine pass past the far post.
And that first-half moment proved crucial for the striker who has vowed to be more clinical should the occasion arise again.
He said: ‘They nullified our work a bit.
‘We struggled to break them down but that is something we will have to look at and improve on when teams do camp here.
‘We had a couple of chances.
‘I had one and Westie (Westcarr) had one.
‘I should have put mine away but I think we have got to keep our heads up now.
‘It was a great ball from Jed and I should have put the chance away.
‘It was just wide. I was thinking about volleying it first time but that would have been a bit of a dodgy one.
‘Obviously if I had put that away it might have been a different game, but as a striker, when you do miss a chance you have to try to forget about it and be ready for the next one.
‘I didn’t get the next chance in the game but tomorrow I may get a similar chance and will be ready to put it away.
‘We have all got to try and learn what we did wrong against Newport and see where we can improve ready for a tough game against Yeovil tomorrow.’