It appeared the Blues were heading for a rare point on their travels when Andre Dozzell netted in the 80th minute to cancel out Mihailo Ivanovic’s opener.
However, with two minutes of normal time remaining, Ivanovic headed home Casper De Norre’s precise cross from the right for his second and Millwall’s winner.
It was more frustration for John Mousinho’s men who lost in similar circumstances at Preston in their previous away match. And here are our Pompey player ratings...
5. Cohen Bramall - 7
(Replaced by Marlon Pack on 69 mins) Reined in his useful forays down the left and focused on defending, which he did solidly. His pace and mobility are big assets, always providing a useful safety net. Photo: Jason Brown
6. Andre Dozzell - 8 - MOM
Calmly slotted a shot through a ruck of players to level, then later popped up in the Blues’ penalty area to thwart an attack. That summed up what he offers Pompey and it was another tireless display. Photo: Jason Brown
7. Freddie Potts - 7
Not as influential as usual, given little time of the ball through Millwall’s physicality. Work-rate still there, though, and kept on running. Photo: Graham Hunt
8. Matt Ritchie - 6
(Replaced by Harvey Blair on 69 mins) - Helped keen Pompey defensively tight, aided by that magnificent work-rate. Barely made any inroads as an attacking force, although did pop up in the 65th minute to hit the post. Photo: Jason Brown