They were shot out for 79 after winning the toss against Sparsholt and deciding to bat first at St Helens, eventually losing by four wickets.
The hosts had lost half their wickets with only 18 runs on the board, and they were indebted to Jack Marston (31) who was one of only two batsmen to hit double figures.
Open Jordan Palmer-Goddard was dismissed for a duck by Joshau Williams (3-6 off five overs).
Portsmouth then lost three wickets with the score anchored on 13 - skipper Ben Duggan (9) and Tom Wallis (0) also clean bowled by Williams and Dan Wallis (4) bowled by Thomas Ley (2-15).
Marston and Alex Hammond (13) shared a 49-run stand for the sixth wicket but Dan Sumner (3-9) and Jeremy Frith (2-15) ensured the tail didn’t wag.
Joe Kooner-Evans ensured Sparsholt didn’t have it all their own way when they replied.
The seam bowler bagged 4-21 as the visitors were reduced to 40-5, giving Portsmouth renewed hoe.
But opener Frith (42 not out) and Tim Simmonite (11) added 39 for the sixth wicket as Portsmouth, who were among the promotion contenders in 2019, remained fourth from bottom.
Sarisbury’s Ricky Rawlins produced a superb innings to give his side a crucial victory in the battle to avoid relegation.
Asked to chase rock bottom St Cross 2nds’ 164-9 total, Sarisbury - just above the two-team drop zone - crashed to 34-9 (Aaron Hockey 3-15).
But former skipper Rawlins, who has mainly opened in the past but here was batting at No 5, came to the rescue with a sparkling unbeaten 84.
He put on an unbroken 56 for the seventh wicket with Michael Bond, whose 16 not out was the second highest scorer after Rawlins.
Rawlins took three fours off the 38th over - bowled by Cameron Braans - as 16 runs came from it in all.
A further eight came off the 39th, bowled by Harry Foyle, with Bond striking the winning boundary off the final delivery.
Sam Hill (3-23), Tom Kitcher (2-26) and Jordan Wright (3-26) had helped restrict St Cross after they had elected to bat, Michael Howath (56) top scoring.
Jon Hudson starred with bat and ball as Waterlooville put some daylight between themselves and the Division 2 relegation zone.
Ville had slipped to third from bottom after losing six times in seven matches, but Hudson’s heroics helped them beat Old Tauntonians & Romsey by 61 runs.
First, Hudson top scored with 47 in a total of 132-9. Ville had slithered to 40-4 before Hudson and Sonny Reynolds (22) added 60 for the fifth wicket.
OTs then lost openers Jovan Dhariwal (2) and Bothwell Chapungu (1) cheaply to fall to 3-2.
Hudson the wreaked havoc with the ball, taking three wickets as OTs crashed from 18-2 to 22-5.
It was 36-6 when Hudson (4-12) struck again, dismissing top scorer Harry Tulk (23).
With Sam Robinson taking 2-10, OTs the early-season league leaders - were routed for just 71.