Kenny Jackett has pledged to ‘eradicate’ Pompey’s growing last-minute vulnerability.
Joe Mattock was the match-winner deep into stoppage-time as Rotherham inflicted a heart-breaking defeat on the Blues.
I haven’t necessarily got one particular thing I can put my finger on for it, but it is something we have to eradicateKenny Jackett
It represented the third time in four matches Jackett’s men have been undone by a late goal.
On New Year’s Day, Liam Sercombe secured a dramatic victory for Bristol Rovers, while there was a 2-1 Checkatrade Trophy loss at the hands of Chelsea under-21s courtesy of Charly Musonda.
At the New York Stadium on Saturday, it appeared Pompey had earned a gutsy point – before Mattock’s intervention.
And Jackett is determined to get to the bottom of the recent trait which threatens to undermine a highly-encouraging season.
He said: ‘It’s very frustrating. I cannot necessarily put my finger on one thing but it’s something we have to eradicate.
‘If you look at Bristol Rovers, Chelsea under-21s and now Saturday, all had goals in injury time and all were crucial ones as well.
‘At that particular moment it is down to either wrong decisions or not being able to see it out. That has affected three of the four of the games – and that is a fact.
‘I haven’t necessarily got one particular thing I can put my finger on for it, but it is something we have to eradicate if we want to keep competing at the top end of this league.’
Meanwhile, Jackett insists Pompey are not close to strengthening their squad.
Connor Ronan and Sylvain Deslandes are the only Fratton Park arrivals during the January transfer window.
The Blues boss added: ‘Is there anything close? No, there’s not.’