Wiebe, who won the Senior British Open Championship two months ago, skillfully played the blustery breezes at Kapolei Golf Club en route to the lead.
Meanwhile, Singh -- making his Champions Tour debut -- charged into sole possession of second place at minus-9 with a 6-under 66, notching the low round of the day.
Sharing third at 8-under were Brian Henninger (69) and Corey Pavin (68).
Cook (71) and Sandy Lyle (67) were tied for fifth at 7-under.
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