Michael Appleton insists his Oxford United side will not be targeting a draw in their Fratton Park visit.
The U’s head to the south coast on Saturday for what is expected to be an 18,931 sell-out.
Appleton’s third-placed team are four points ahead of the Blues and suffered a home defeat to fellow promotion rivals Bristol Rovers last Sunday.
Regardless, the ex-Pompey boss claims he will not be setting them up to clinch a Fratton draw.
He said: ‘The frustration against Bristol Rovers was when you’re playing the teams up around you the important thing is to make sure you can get something out of the game.
‘It probably would be a better point for us than Portsmouth, but if you look at the way we played on Sunday we were always trying to get the win.
‘I don’t think we’ve got it in us to take a point.
‘To be fair, at this time of the year are points that useful to you? I’m not too sure, I think it’s about the three points.’
Appleton managed Pompey for almost a year before his November 2012 departure for Blackpool.
During that time the club went into administration, were deducted 10 points and then relegated to League One as they battled to stay afloat.
Appleton won 14 of his 51 matches in charge, yet until his exit was largely a popular figure among supporters during some tough times.
After a short spell at Blackpool, he moved to Blackburn, which was just as chaotic, and Oxford brought him back into management in July 2014.
He returned to Fratton Park for the first time since leaving when his U’s side collected a goalless draw in February 2015.
Now he is set for another reunion as both sides target the promotion spots in what is developing into a fascinating race.
And he believes the Oxford players will not be intimidated by tomorrow’s bumper Fratton crowd.
He added: ‘Most sides in our division probably see playing away to Portsmouth as the most difficult away game, just because of the atmosphere generated at Fratton Park.
‘There will probably be 17 or 18,000 people there and I’m sure we’ll have fantastic support.
‘But you can almost enjoy that and thrive off it.
‘The fact is we go there as underdogs as most teams would do, but I think our players really enjoy the big games.
‘I say it all the time but you can’t always guarantee a result – such as last Sunday – but if we get the performance we put in there again I’d be surprised if we don’t come out of the game with something.’
Meanwhile, there will be no Fratton return for Ryan Taylor tomorrow.
The former Blues striker is sidelined by a groin problem which has troubled him this season.
Taylor scored 16 goals in 59 appearances before leaving Pompey last summer.