Marcus Harness struck the woodwork before Jack Bonham made key saves to deny Ellis Harrison and Harvey White.
But when Pompey finally did break the deadlock against Gillingham at Fratton Park, their lead lasted for only eight minutes.
Sean Raggett had headed home following fine work from Harness, only for Vadaine Oliver to capitalise on a rare Lee Brown error to level.
And the hosts were unable to find a winner after the break, with Kenny Jackett admitting that their opponents looked the more dangerous side in the closing stages.
The Blues boss said: “We played well in the first half, worked their goalkeeper a lot and also hit the post, but a defensive mistake has allowed Gillingham back into the game.
“I thought we should have been ahead at the break because we showed some good patterns of play and combinations.
“But we lost our way a bit in the second half and our opponents really had the last 15 minutes of the game.
"We needed to be better in certain moments to get our noses in front and have to keep persevering, but it was a frustrating day for us."
“There was a big decision on the hour mark, with Harvey White’s appeal for a penalty and after that it was tough for us.
“Gillingham had some good chances and our keeper made an excellent save from John Akinde. By the time the game concluded, we were pleased with a point.
“We needed to be better in certain moments to get our noses in front and have to keep persevering, but it was a frustrating day for us.”
Teenage defender Haji Mnoga was handed just his second league start for the club in place of Callum Johnson.
Jackett explained: “Callum has a calf injury and we think he’ll be out for around two or three weeks, while our other recognised right-back James Bolton has an ankle problem.
“We think he might be alright for Tuesday night, but it opened up an opportunity for Haji to come in and play.
“It’s difficult because there’s been so little football due to Covid-19 in terms of under-23 games, but he did well and has a lot of natural ability.”