Mantz, a junior from Smithfield, Utah, rallied to keep it close and then blew the doors off the competition at the 2020 NCAA Division I Cross Country Championships in Stillwater, Oklahoma. Trailing by as many as five seconds at the 4K split, Mantz drew even at the 7K split and then gapped the field to eventually win by 22.1 seconds in 29:26.1. Earlier in the season, Mantz also crossed the finish line first at the West Coast Conference Cross Country Championships and the Silver State Collegiate Challenge. He finished runner-up at the Oklahoma State Invitational.