The Rugby Camp side have lost seven matches this season – and six of them have been by eight points or less.
That includes a 23-22 defeat against tomorrow’s hosts on home turf at the start of the campaign.
Assistant coach Jim Pearce believes his team are capable of turning the tables on their Hampshire rivals.
And he insists the key to winning is mental rather than physical.
Pearce said: ‘It has been shown in this league there are fine margins for error.
‘If we had been able to turn the six-point losses into wins or bonus points, potentially we could be at a different end of the league.
‘Turning the close games into our favour is a skill we must cultivate.
‘The players need to be in the right frame of mind and maintain their concentration from the start.
‘Our last game, at Old Reigatian, is a prime example.
‘We found ourselves 17 points down after only 20 minutes, got back to lead 19-17 only to lose it at the death.
‘You cannot afford to give a team second in the league a 17-point start.
‘We have to learn how to start games and how to close them out when we are in front.
‘The players can’t afford to leave themselves in the changing room.’
Matt Farnes, who made his debut at outside-half at Old Reigatian, is unavailable, so Simon Morgan is drafted back in.
Curtis Barnes starts on the wing in place of the unavailable Alex Duffs.
New recruit Luke Peters, from United Services, takes his place on the replacements’ bench.
In the forwards, rotation means that Anthony Fooks comes in and Rhys Bowen drops down.
Portsmouth are hoping to repeat last season’s win at Winchester as they head into the Christmas break.
Pearce added: ‘This is the first of the reverse fixtures, so it is important to make a good start to the second half of the season.
‘In our games so far, we have not been clinical enough in our execution or concise enough in our thoughts.
‘Since the start of the season we have been trying to adapt our style of play to enable the players to utilise their strengths.
‘Our set-pieces have been relatively good and once we got going at Old Reigatian we dominated physically.
‘The players have shown they are committed to the cause by agreeing to train over the holiday period.
‘We have a packed start to the new year because of cup commitments.
‘Success in the RFU Intermediate Cup and the Hampshire Cup, hopefully, will give us added momentum in the league games.’
Portsmouth: Davies, Barnes C, Gates, Richards, Whitehouse, Morgan, Ellis, Clark, Hoolihan, Wilkie, Crabb, Giquel, Kelly, Fooks. Replacements: French, Bowen, Leonard