"He was the most consistent throughout fall camp," coach Dennis Erickson said.
Erickson said that Osweiler will play in the opener against Portland State on Saturday, though how much time he'll get has yet to be determined.
The 6-foot-5, 240-pound Threet started eight games for Michigan in 2008. He passed for 1,105 yards, completing 51 percent of his throws, with nine touchdowns and seven interceptions. He also rushed for 201 yards.
Threet, who sat out last year per transfer rules, was the favorite before spring practices began but Osweiler surged and seemed to lead early in fall camp. But over the last week, Threet found his rhythm.
After Portland State, the Sun Devils play Northern Arizona, another FCS school. That should give Erickson,who called it a close competition, the security he needs to experiment before heading to Wisconsin on Sept. 18.
"We'll play them both to start out and see what happens," Erickson said.
Ted Miller is the Pac-10 blogger for ESPN.com.