Frost (left) and Calcavecchia hold a two-shot lead over three players.
BLAINE, Minn. (AP) -- David Frost shot a 6-under 66 and was tied with Mark Calcavecchia for the lead after two rounds of the 3M Championship.
John Cook (67), Kirk Hanefeld (64) and David Peoples (66) were two shots back.
In his fifth tour event since turning 50 on June 12, Calcavecchia started the day one shot behind Tommy Armour III, but birdied six of his first 10 holes to open up a three-shot lead.
Calcavecchia's lead shrunk to one before back-to-back birdies on the 15th and 16th. But he had bogeys at No. 17 and another at the par-5 18th, which ranked as the day's second-easiest hole, to finish with a 66.
His second shot went into a greenside bunker and his chip went about 75 feet past the hole. He three-putted from there.
Playing with Calcavecchia, Frost made three birdies in a four-hole stretch on the front nine, before going eight holes without another. He made two more in the final four holes.
Cook, who tied for third at last week's U.S. Senior Open, shot a 5 under 67. He was 3 under on the front nine and made birdies at Nos. 13 and 15 to get within one shot of Calcavecchia before a bogey on No. 16.
Hanefeld, who has one top-25 in 10 starts this year, was 4 under on the front, and birdied No. 10, 11, 16 and 18. He hit every green and fairway in regulation.
Steve Haskins eagled No. 18 for a 66, and is joined by Jeff Sluman (68) three shots behind.
Armour was just 1 under for the day, and joined at -- under by Mark O'Meara (66), who birdied seven of eight holes in one stretch, Ross Cochran (67) and Bruce Vaughan (67).
The openness of the TPC Twin Cities has been a welcome relief for tour players. The last two events were the British Senior Open in Scotland and the U.S. Senior Open at Sahalee Country Club outside Seattle, two unforgiving tracts were poor shots equaled poor results.
A few sprinkles fell on the course early in the day before humid conditions took over, further softening the greens and allowing players to take aim directly at the pin, just as they did Friday.
Defending champion Bernhard Langer likely won't repeat. He is one of four players that are seven shots back. No champion has defended his title in the event's 18-year history.