Pompey looked like they had seen off the onslaught to claim a point at Rotherham.
Their opponents had controlled the second half, with a series of crosses being sent into the visitors’ box.
But a combination of solid defending and brave blocks repelled the threat – until the first minute of stoppage-time.
Substitute Michael Smith sent a cross into the box for Joe Mattock – a fellow former Fratton employee – to head home.
And Kenny Jackett was frustrated to see his side concede in the dying moments for the third time already in 2018.
The Blues boss said: “There have been a few late goals that have cost us now and that’s obviously disappointing.
“I thought that we’d ridden the storm in the second half and the game appeared to just be petering out.
"We didn’t go ahead and then it was an onslaught following the restart with a lot of set-pieces – it was hard for us to handle."
“We’d contained Rotherham well before the break and actually created the best chances, with Pitman’s header, Lowe’s shot and a volley from Naismith.
“They were three clear-cut opportunities for us, compared to a minimal amount of threat from them at the other end.
“But we didn’t go ahead and then it was an onslaught following the restart with a lot of set-pieces – it was hard for us to handle.
“There were some promising situations on the break, but we just couldn’t get on the ball and capitalise on that.
“We battled and scrapped very well, though, and I thought we’d come through it with a very spirited bunch of players.
“So it’s obviously very frustrating for us to concede a goal in injury-time and that has cost us a point.”
Sylvain Deslandes was handed his Pompey debut at New York Stadium following a loan switch from Wolves earlier in the month.
Jackett said: “He’s a strong, competitive lad and I felt he did well. He tired a bit in the second half, but that’s to be expected because he hasn’t played much this season.”