Mediate fired a 4-under-par 67, finishing at 17-under 196. He eagled the par-5 15th Saturday after doing the same on the par-4 fourth in round two and collecting a hole-in-one Friday on the par-3 third hole.
His latest round put him three shots ahead of Bo Van Pelt, who registered a 6-under 65.
Rickie Fowler found himself alone in fifth place at minus-11 after firing a 3-under 68 Saturday.
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