Purbrook face a promotion showdown with South Wilts II in division three of the Southern League.
The winner-takes-all encounter will decide who climbs into division two alongside champions Fair Oak.
Purbrook, who begin the game in second spot, will need to improve on last week’s performance in defeat to Fawley.
Vice-captain Martin Lee said: ‘We were shocking with the bat. In fact, it had been coming because we haven’t posted a massive score for a while.
‘We have been defending lowish totals to get ourselves over the line.
‘Hopefully, we are due a big score.
‘We have not batted to our true potential.
‘If we had won at Fawley then we would have been promoted.
‘So this is probably a bigger game than the one when we got promoted from the Hampshire League.
‘Now we have got to do it on the final day. If we are good enough then we will do it.’
The arrival of Josh McCoy at the start of the season made a big difference to the team.
The former Hampshire Academy all-rounder is the leading runscorer (560) and wicket-taker (29) in the side.
‘It is very handy having someone of his quality in the team,’ added Lee.
‘He should be playing a couple of levels higher but was happy to come and enjoy his cricket with us.
‘Our performances in the second half of the season have proved we are good enough to go up.
‘At one stage we put together six successive wins.’
Portsmouth & Southsea finish their first season back in the Southern League at home against Fawley.
Batting has proved their strength – with Jack Davies (584) and Matt Benfield (492) in the top three runscorers in the division.
They are only separated by McCoy at the summit.
Havant II need to beat Bashley II at Havant Park to stand any chance of avoiding relegation.
In division two, Waterlooville could secure a top-four finish by beating Basingstoke & North Hants II at Rowlands Avenue.