Victory for the Gulls against Perth at Dorrien Gardens would have allowed them to usurp the Azzurri in third spot.
But the hosts held off the challenge for their ladder position with a 2-0 win.
Perth slotted two goals in the first half with Sorrento unable to respond despite a number of chances in the second.
At ECU Joondalup Football Stadium, the Jacks suffered their worst loss of the season in a 7-2 defeat to second-placed Floreat Athena.
The hosts were down 2-1 at half-time but the flood gates opened in the second half as Floreat piled on five goals.
ECU plays Armadale away and Sorrento is home to Bayswater on Saturday.