With Kevin Neave, Steve Berryman and Kevin Lockwood all making half-centuries, St Cross posted a handy 230-3.
But after losing two quick wickets, P & S took command, with the Benfield brothers Matt (111), pictured, and Tom (56) sharing a sizeable partnership.
St Cross took seven P & S wickets, gifting their hosts 24 no-balls (four extra overs) before they clinched the title with an over to spare.
P & S finished five points ahead of runners-up Lymington II, who have bounced back to the Premier League at the first attempt.
They thumped Hook & Newnham Basics II by 134 runs, while Longparish had their work cut out in beating Rowledge II by three wickets.
Luke Watson smashed a league best 135 as Fareham & Crofton piled up 311-6 against nine-man Ventnor II at Steephill. Ventnor are relegated alongside the second teams from New Milton and Sarisbury Athletic.
Parley clinched the County 2 title when they ran up a hefty 332-7 before winning by 149 runs at Redlynch & Hale.
Easton & Martyr Worthy thrashed Ferndown Wayfarers to finish second, while Totton & Eling II and Ellingham are among the teams to go down.
Odiham & Greywell are County 3 North champions, with IBM Hursley take the South crown, the pinnacle of a fantastic season for the entire club (see separate story).
* The various championship successes in the HCL will be reviewed individually in the coming week or so.