The south-coast side thrashed Glamorgan on Sunday and director of cricket Giles White believes they can build on that to grab a vital win in the race to reach the quarter-finals.
He said: ‘Our batting was excellent at Swansea, with Liam Dawson setting a great example as captain and showing what he is capable of at the crease.
‘Our seam-bowling has been really effective in recent matches and that’ll be a key factor against Somerset, who have been formidable with the bat in 50-over cricket this summer.
‘The team is in a good place and Sunday’s victory has boosted confidence going into this important game.’
Predicted Portsmouth XI v Cheltenham: changes expected to side that beat Cardiff so handsomely - but attacking duo could keep places and defender set to return
League One latest: Oxford land former Pompey striker target from Swansea as Sheffield Wednesday bemoan exciting duo's move to Brentford and former Peterborough boss criticises club
Portsmouth boss Danny Cowley hails Spurs loanee Dane Scarlett as move already shows signs of putting Miguel Azeez's short stint from Arsenal in shade
Former Portsmouth keeper Alex Bass suffers tough night on and off the pitch as he makes Sunderland debut following Fratton Park exit
Portsmouth transfer news: Blues youngsters attracting interest but Danny Cowley has no desire to cash in just yet
Hampshire need to win against Somerset and have a better competition run-rate than two of Kent, Surrey and Middlesex to ensure qualification.
However, just a win over Somerset, regardless of competition run-rate, could be enough if other results go their way.
If Hampshire win and better the results of Kent, Surrey and Middlesex, and Essex lose to Gloucestershire, Hampshire will secure a home quarter-final.
They could still qualify for the quarter-finals with a defeat to Somerset, but other results need to go their way.
Dawson will lead the side again after scoring an unbeaten century off 69 balls at Swansea.
Will Smith, Ryan McLaren and Tom Alsop have all been in top form as well.
While Brad Wheal, 19, took four for 38 against Kent Spitfires at the Ageas Bowl on Tuesday.