The Salt Lake City-based Spiders (11-3-2) are the first team outside California to win the WPSL, an amateur league that serves, along with the W-League, as a Second Division to the WUSA.
The Storm are the only two-time WPSL champion, winning in 1999 and last season.
Amber Brower also scored for Utah, which was invited to the final four only after the Denver Diamonds -- the wild-card qualifier -- were unable to pay their league dues nor arrange a flight to the Bay Area in time for Saturday's semifinals.
Utah, coached by former Spiders forward Joanna Barney, surprised U.S. Women's Open Cup champion Ajax Southern California in the semis, with Reading, a former BYU standout, and Brower, a University of Utah senior, scoring in a 3-1 victory.
Brower tallied in the 15th minute Sunday, but former San Jose State forward Stacie Alberico pulled the Sacramento-based Storm (10-1-4) even in the 74th with her 12th goal of the season. Reading's winner arrived in the 90th minute.
Former Storm forward Kim Patrick, a University of Tennessee product who signed earlier this month with the WUSA's San Jose CyberRays, won the scoring title with 31 points. She shared the league lead in goals (12) with Alberico and assists (7) with Ajax's Isabelle Harvey, a former Canadian national-teamer and USC standout.
1998 -- Silicon Valley Red Devils
1999 -- California Storm
2000 -- San Diego WFC
2001 -- Ajax Southern California
2002 -- California Storm
2003 -- Utah Spiders
WPSL FINAL FOUR
at San Francisco
Semifinals (July 26)
California 3 (Alberico 41, Williams 44, Tate 63) New England 1 (LeDuc 35).
Ajax Southern California 1 (Harvey 24) Utah 3 (Reading 7, Brower 10, Mattes 26).
Final (July 27)
California 1 (Alberico 74) Utah (Brower 14, Reading 90).