Armour, who had two victories in more than 20 years on the PGA TOUR, has three second-place finishes in 12 previous starts during his rookie year on the Champions Tour.
Starting on the back side, Armour birdied three of his first four holes and added another at No. 18. Birdies on Nos. 2 and 3 got him to 6-under par, before he birdied his last three holes. Armour, who ranks 10th in Tour putting average, one-putted for seven of his birdies.
Calcavecchia, who also started on No. 10, was 2 under through 10 holes, before he birdied No. 2 and eagled the par-5 3rd and par-5 6th. The latter came when he chipped in from a greenside bunker.
Playing in a group with Calcavecchia, Frost was 3 under at the turn, before four straight birdies on the front side. Frost, who switched back to his old putter before the round, made a 40-foot putt at No. 8 to get to 8 under.
Defending champion Bernhard Langer--the winner of senior major tournaments the last two weeks--is one of nine players that are five shots back. No champion has defended his title in the event's 18-year history.
On a perfect day for golf--temperatures in the low-80s, partly cloudy skies and little wind--45 of the 78 players finished under par at the TPC Twin Cities.
Fred Couples and Minnesota native Tom Lehman, who are second and third in the season-long Charles Schwab Cup points standings, are not in the field. Nor is Corey Pavin and Tom Watson, also in the points top 10.