Kenny Jackett admitted he believed the first goal was going to be key in deciding the destiny of their FA Cup trip to Luton.
James Collins’ crisp strike in first-half stoppage-time clinched a 1-0 victory for the Hatters this afternoon.
Pompey had their opportunities to level, mainly during a pulsating second half, but found home keeper Marek Stech in inspired form, while Matt Clarke’s header struck the bar.
Yet the equaliser would not arrive, while the Blues also had to see out the final six minutes at Kenilworth Road with 10-men following two yellow cards for Nathan Thompson.
And Jacket was left to nurse four successive defeats and a team without a goal in three matches.
He said: ‘I felt it was an end-to-end game and the first goal was always going to be key.
‘We looked pretty comfortable defensively for the majority of that half and have been caught in their right-back position and some one-touch football has got them a key goal, which was the difference.
‘We had spells, we had chances, we had good opportunities and couldn’t find that cutting edge, but in the end they just edged us out.
‘We must work very hard to keep the players’ confidence high and keep them determined and not sorry for themselves, focusing on Charlton in the Checkatrade on Tuesday and then Blackpool away.
‘It’s a disappointing run of results.’