The Griffons (2-0, 1-0 MIAA) torched the Miners for 462 offensive yards, and allowed just 51 rush yards defensively.
Fenwick took the head coaching job at S&T in the off season after serving as Western's offensive coordinator for six seasons.
The Griffons came up empty on their first two possessions of the game, but were provided a spark by defensive back Marc Harrison. Harrison picked off Reed Brown's pass and returned it 25 yards into Miner territory.
Western capitalized on a 11-yard touchdown run for Travis Partridge.
Missouri Western picked up 331 yards on the ground -- 107 and two touchdowns coming from running back Raphael Spencer.
The Miners turned the ball over for a second time on a muffed punt in the second quarter. Spencer followed with a 41-yard touchdown run on the next play.
Missouri S&T dug an even bigger hole in the second quarter when Missouri Western's MacKenzie Wischmann blocked a punt, and Darrian Bass scooped the fumble and returned it six yards for a touchdown.
Dee Tolliver led the Griffons with three receptions for 60 yards, including a 34 yard touchdown.
Missouri Western plays its second road game September 21st against Nebraska-Kearney.