St. Thomas went into Saturday's home game against unbeaten Concordia (Moorhead) with the top scoring offense in the MIAC.
But the Tommies relied on their defense, instead, to defeat the Cobbers 21-0 and take over sole possession of first place in the conference standings.
The Tommies, ranked No. 6 in the AFCA Division III poll, limited the No. 15 Cobbers to 108 yards and six first downs.
The Tommies (5-1, 4-0 MIAC) held the Cobbers (4-1, 2-1), who were leading the MIAC in rushing (271.5 yards per game), to 78 yards rushing.
The Tommies defense set up each of their three touchdowns.
In the first quarter, Adam Brant recovered a Cobbers fumble to give the Tommies possession at the Cobbers 43-yard line. Trettel capped the drive with a 9-yard TD run.
After the Tommies forced the Cobbers to punt from their own 16-yard line, they took over at midfield. Six plays later, Jacques Perra threw a 27-yard TD pass to Jackson Hull.
Early in the third quarter, Brant recovered another fumble at the Cobbers 25 and returned it to the Cobbers 2-yard line.