Hill belted an unbeaten 37 off just 15 balls as Athletic claimed a five-wicket win over Division 1 promotion rivals Rowledge.
Sarisbury are now 29 points clear of Alton at the top of the table, with five weeks remaining.
On course, therefore, to return to the Premier Division where they previously spent one season, in 2015.
Asked to chase 186 for victory, Sarisbury lost opener Tom Mills for a third-ball duck while Ricky Rawlins (11) and Cameron Grierson (6) also fell cheaply.
But Athletic’s leading runscorer Sam Floyd took his seasonal SPL tally to 539 - only Ventnor pair Martin Blackman and Dinesh Thimodya have scored more - with 55, his fifth half-century of the league campaign (plus a century).
Hill, batting at No 7, and Matt Journeaux (29 not out) - the latter playing only his second 1st XI game for the club since 2019 - added an unbroken 56 for the sixth wicket.
With Hill belting three sixes and three fours, Sarisbury won with almost 15 overs to spare.
Rob Franklin (3-19), Ronan DeGrussa (2-14) and Jordan Wright (2-47) had reduced visiting Rowledge to 97-6.
A stand of 43 for the seventh wicket between Zak Le Roux (73) and Will Ryman (21) was the highest of the innings as Rowledge were bowled out for 185 (Journeaux 2-38).
Portsmouth posted 214 at Alton - the highest total by a side batting first in the second tier on the day.
But it still wasn’t enough, though, as the hosts leapt above Rowledge into second spot with a three-wicket win.
There were just two balls remaining when Bash Walters hit the winning run off the bowling of Joe Kooner-Evans, having struck the preceding delivery to the boundary.
Captain Scott Myes (83) and Daniel Harris (53) had helped Alton reach 188-4.
Portsmouth skipper Ben Duggan had elected to bat, but was one of the wickets to fall as his side plunged to 50-4.
There followed an 83-run stand for the fifth wicket between Minhaj Jalill (49) and wicket-keeper Sujeeth Daini (41). Zach Gadsby’s 4-37 haul included the wicket of Daini.
Mid-table Portsmouth host Sarisbury at St Helens next weekend.