Junior guard Vel Williams added 14 points, eight assists and five steals and sophomore guard Melissa Keiser scored 12 points for the Tommies.
Junior forward Rosinta Stromquist had a season-high 16 points and 10 rebounds and junior guard Rachel Cherry added 10 points for Augsburg.
Opdahl had 13 points and 10 rebounds in the second half and recorded her ninth career double-double. The Toms completed a season sweep of the Auggies and ran their win streak in the series to 40 dating backto 1985.
The Toms led just 27-25 before a 12-0 run helped build a 39-30 halftime lead. St. Thomas used a 15-5 run to open the second half and never led by less than 12 thereafter.
St. Thomas survived 12-of-27 foul shooting and shot 44% (30-of-68) from the field. They made seven 3-point baskets, their second highest total of the season, while Augsburg made only 1-of-12 from beyond the arc.
Augsburg shot 33% from the field (24-of-73) and made only 11-of-22 at the foul line.