Williams found Brandon White for a 74-yard scoring strike in the first quarter and Reggie Bell for a 61-yard touchdown in the second quarter. Williams finished 12 of 25 for 203 yards. White had five catches for 122 yards, while Bell made five catches for 78 yards.
San Diego (1-0) led 23-3 early in the third quarter after an 11-yard touchdown run from Jonah Hodges. Hodges had 120 yards on 23 carries.
But Western New Mexico - a Division II school - didn't go quietly. Mitch Glasmann's two fourth quarter touchdown passes - of 15 yards to Marcus Smith and 31 yards to Donald Byrd - cut the deficit to six points.
Western drove to the San Diego 17 with 17 seconds left, but Glasmann's pass intended for Smith fell incomplete.