The teams endured a 30-plus minute weather delay midway through the first half.
Heimer recorded a goal and an assist. UST had a 4-1 edge in both corner kicks and shots on goals.
St. Thomas (9-1 overall, 5-0 MIAC) remains alone in the conference lead by one half game.
Coach Sheila McGill's Toms ran their victory streak to nine, the longest for St. Thomas Women's Soccer since 2001. The Toms have outscored opponents 32-3 during the win streak.
St. Thomas plays three games in a four-day span starting Saturday afternoon at Carleton.