It was a soft goal to concede and made for an uncomfortable ending at Bloomfield Road.
But Kenny Jackett took solace from the fact it was the first time Pompey have conceded in their opening two matches this season.
The Blues appeared to be seeing out a comfortable 2-0 victory at Blackpool on Saturday.
However, the hosts grabbed one back nine minutes before and got themselves back into the game.
A long ball forward from Tangerines keeper Mark Howard split the Pompey defence, with Mark Cullen reacting first and lobbing his finish over Craig MacGillivray and into the back of the net.
Although Jackett admitted it was a poor goal to let in, he’s generally been pleased with his side’s rearguard performances so far this term.
The Pompey boss said: ‘We gave a poor goal away. We started to go to deep and we’ve let their guy in behind us.
‘The guy has been able to run straight through which is one of those were he can’t be offside.
‘If we didn’t give that goal away then we would have got that clean sheet.
‘But, overall, giving one goal away in two games is very good.
‘Had the kick come out of the keeper’s hands then it might have been different.
‘However, we can't stop everything. To conceded one goal in two games is excellent and something we need to build on.’
Blackpool’s equaliser meant they had their tails up and pressed for an equaliser.
Cullen thought he’d snatched the Seasiders a point in stoppage-time when he bundled the ball into the net.
However, the assistant referee’s offside flag curtailed the home celebrations.
Jackett is convinced it was the right decision.
‘It was definitely (offisde),’ added the Blues boss.
‘As their fella got the first flick, he was in the offside position.
‘Had he not touched it, I think Craig would have got to the ball anyway.
‘Their man was in a no-win situation, really.’