Pompey fans have been warned there will be no pay on the day option for the trip to Mansfield on Saturday.
So far more than 950 visiting tickets have been sold for the Field Mill encounter.
Of the 1,500 allocation for Blues followers, there remain around 550 left on sale.
However, Mansfield have stressed away supporters will not have the facility to pay on the gate on Saturday.
Instead, all tickets must be purchased in advance from Pompey, either through the ticket office or the online system.
It means fans have until close of business tomorrow to get their tickets in person from Fratton Park, which is usually around 5pm.
After that they will be unable to purchase seats in the away end situated in the North Stand for the fixture at the Stags.
The Field Mill ticketing system contrasts with that of Accrington Stanley, Pompey’s only other away match so far this season.
On that occasion, fans were allowed to pay on the day at the Crown Ground, attracting a visiting attendance of 1,001 despite the 12.15pm kick-off and the match being televised.
Pompey’s last visit to Mansfield was September 19, 2006 in the Carling Cup.
Harry Redknapp’s side ran out 2-1 winners that day thanks to goals from Manuel Fernandes and Matt Taylor.
The last league encounter between the sides was on May 2, 1977, when Mansfield won the division three battle 2-0.
The Stags were promoted after that result while Pompey boss Ian St John was suspended from duties afterwards, with Jimmy Dickinson taking over.
Prices for Saturday’s match are £18 for adults, £13 for seniors and full-time students and £8 for juniors (seven to 16). Children under seven go free.