Gary Roberts says Pompey are preparing for a momentous match at Accrington on Tuesday evening.
The Blues will leapfrog their opponents into fourth spot in the League Two table with victory at the Wham Stadium.
It would also see them close the gap on the automatic promotion places to just six points.
But Roberts knows that Pompey will not find it easy to beat a club who he made 67 appearances for earlier in his career.
The midfielder said: “I think it’s the biggest game yet. A win would see us move up a position with only 11 matches to go and put some pressure on the sides above us.
“Sometimes people go to Accrington and think it won’t be pretty, but they play a great brand of football.
“They’ll get the ball down and try to play the right way, so it’s going to be a tricky test for us. I certainly don’t think it will be a battle.
“If we get three points there then it stands us in good stead for the sprint home, but right now we can’t look past Accrington.
“They gave me a chance to play full-time football, so I’ve got a lot to thank them and John Coleman for.”
Roberts knows that Pompey will have to string together successive victories if they are to break into the top three before the end of the campaign.
He said: “We’ll probably have to win more than three in a row because the teams above us don’t lose many.
“It’s going to take a lot of victories, but when I look around our dressing room, I don’t see why we can’t do that.”