The Storm topped the New England Mutiny, 3-1, and will face the Utah Spiders -- 3-1 winners over Ajax Southern California -- in Sunday's title game at Kezar.
Alberico tallied in the 41st minute, her 11th goal of the season, and Williams struck in the 44th as the Sacramento-based Storm turned a 1-0 deficit into a 2--1 halftime lead. Katie Tate added a goal in the 61st minute.
The Mutiny, a former W-League club playing its first season in the WPSL, went ahead on Rachel LeDuc's 35th-minute goal.
Utah stunned Ajax, last year's runner-up, with two goals in the first 10 minutes and owned a 3-0 advantage by the 26th minute. Sara Redding scored in the seventh, Amber Brower in the 10th and Megan Mattes in the 26th for the Spiders.
Former Canadian national-teamer Isabelle Harvey scored Ajax's goal in the 69th minute.
Utah gained the wild-card berth to the WPSL final four when the Denver Diamonds -- the wild-card qualifiers -- were unable to pay their league dues nor arrange a flight to the Bay Area in time for Saturday's matches.