Jay Haas, who sits atop the Champions Tour's money list and Schwab Cup points race, was one stroke back along with five others at the TPC of the Twin Cities.
Fifty-seven of the 78 players broke par on a day with low humidity and temperatures in the 80s. The wind, which can play havoc on the former sod farm, wasn't a factor.
The average score was 69.83, the lowest first-round figure in the event's 15-year history.
'Today, it was duck shooting,' said Thorpe, whose best finish this year was a tie for second in the season-opening MasterCard Championship. 'The golf course is set up for scoring.'
Jenkins' best showing in 2007 was a fourth-place tie at the At&T Champions Classic in March.
Craig Stadler, Bobby Wadkins, D.A. Weibring, John Jacobs and John Harris also had 65s. Three more stood at 6 under, led by three-time champion Hale Irwin.
Organizers are keeping the tournament on schedule despite Wednesday's freeway bridge collapse in Minneapolis. The 54-hole event is being held in Blaine, a suburb about 15 miles north of where the Interstate 35W bridge fell into the Mississippi River.
The tournament initially earmarked charity funds for four local hospitals, and officials said additional money will be given to the local Red Cross in response to Wednesday's disaster.
'It reminds everybody how unimportant golf is in the real world,' said Harris, who is from Minneapolis and wore a black ribbon on his hat to honor the bridge collapse victims. 'It's fun to see everybody out here, but it's been a tough week in Minnesota.'
Haas, who is playing in his first 3M Championship and already has won four events this year on the 50-and-over circuit, set the day's tone along with Stadler when they turned in 65s as part of the day's first grouping.
Haas and Stadler teed off with Bob Gilder at 8 a.m. and finished their round in about 3 hours, 40 minutes. When they left the 18th green, they were three holes ahead of the next group.
Stadler has finished second in the 3M Championship each of the past three years.
David Edwards, the 3M Championship winner in 2006, and Tom Watson, who claimed the Senior British Open title last week in Scotland, shot 69s.