J.W. Walsh went 17-of-30 through the air for 181 yards, one touchdown and one interception for the Cowboys (3-0), whose program came under the spotlight this week amid reports that NCAA sanctions are forthcoming against it.
Sports Illustrated reported penalties are likely as part a probe of Cowboys players allegedly receiving improper benefits dating back to 2001.
The Cardinals (1-2) were held to 124 passing yards.
Kade Harrington led Lamar's ground game with 66 yards on 20 carries.