Frost and Calcavecchia finished with 6-under-par 66s Saturday at TPC Twin Cities in Blaine, Minn., as Calcavecchia stumbled down the stretch to surrender sole possession of the lead.
Leading by three coming into the 17th hole, Calcavecchia carded back-to-back bogeys to end the round. Meanwhile, Frost birdied the 18th, forging a first-place tie at 14-under 130.
The pair held a two-shot lead over Kirk Hanefeld (64), David Peoples (66) and John Cook (67), all of whom were tied for third at minus-12 heading into Sunday's final round.
One shot further back at 11-under 133 were Steve Haskins (66) and Jeff Sluman (68).
First-round leader Tommy Armour III fell into an eighth-place tie with a 71, four strokes back at minus-10.