Guiton took over behind center early in the first quarter after Heisman Trophy contender Miller was hurt when he was pinned between two tacklers. He was carted off to the locker room, later returning to the sidelines wearing a knee brace.
Guiton went 19-of-28 passing for 152 yards with two scoring strikes to Corey Brown and ran for 83 more yards for the Buckeyes (2-0), who reeled off their 14th straight win.
The Aztecs (0-2) got 216 passing yards on 22-of-36 efficiency from Quinn Kaehler.
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