Paul Warne rated Pompey as the best defensive unit to visit Rotherham this season.
The Blues were left floored as they fell to a stoppage-time loss to their play-off chasing rivals on Saturday.
That was after a second-half rearguard action which saw Kenny Jackett’s men defend superbly as they came under heavy pressure.
The Millers had 61-per-cent possession and racked up 10 corners as they put Pompey under the cosh.
The Blues stood firm, however, until the late heartbreak.
Rotherham boss Warne said: ‘I would say Portsmouth are the best defensive team we’ve had here all season.
‘Even if it would have been a 0-0 I think the fans would have appreciated the lads’ efforts. They tried everything they could, threw the kitchen sink. Credit to Portsmouth, they defended really well.
‘I thought our second-half performance merited a win.
‘Goodness knows how many corners we had, we must have had 15! It didn’t seem to drop to the right person at the right time.
‘In fairness, I thought we deserved the win.’
Warne saluted the impact of two former Pompey players as substitute Michael Smith crossed for Joe Mattock to head home the only goal.
He added: ‘There were some really good performances which makes me really proud. The three subs who went on all had a massive impact.
‘The changing room was bouncing afterwards, they’re a really close group and were pleased to get the three points.
‘Smudge (Michael Smith) was excellent. We’re working with him all the time and trying to get him to be the best he can be. I felt he was a real handful.
‘The most pleasing thing for me is Joe Mattock, our left-back, scoring the winner in injury-time.
‘It shows how much the lads want to win and how fit and determined they are.
‘So, it was good scenes at the end of the game for sure.’