Johnson shot a 3-under 69 and Tamulis posted a 2-under 70 to finish regulation knotted at 7-under-par 209.
The win gives Johnson $10,500, which enabled her to jump from 11th to fifth on the Futures Tour money list and give her LPGA Tour card for the 2005 season.
Courtney Wood fired a 6-under 66 and took third at 6-under-par 210. Jimin Kang, the tour's leading money winner and the overnight leader, struggled to a 1-over 73 and came in fourth at minus-5.
Allison Fouch posted a 4-under 68 to tie Lindsey Wright in fifth at 4-under-par 212. Wright, who shot a final-round 73, was second in earnings on the Futures Tour and with this being the final event on the calendar, players were jockeying for the top-five spots on the money list. Those five golfers earn their LPGA Tour cards for 2005.
Along with Kang, Wright and Johnson, two other players earned the LPGA Tour cards for next season thanks to their top-5 finish on the Futures Tour money list. Those two were Nicole Perrot and Aram Cho, both two-time winners this season.
Kang and Perrot were a full-time members of the LPGA in 2003, but were unable to keep their cards. Johnson, Wright and Cho become full-time LPGA Tour members for the first time.