The 56-year-old Lehman birdied three of his first four holes and finished with six birdies and a bogey to reach 4 under. He had a one-stroke lead over playing partner Colin Montgomerie and Brian Henninger.
Lehman won the 2010 tournament in Colorado.
Montgomerie, the defending champion, had a 69, and Henninger shot 67.
Esteban Toledo was 2 under after a 68. First-round leader Massy Kuramoto had a 72 to drop to fifth at 1 under. Peter Fowler, Woody Austin and Jean Francois Remesy were even par. Fowler birdied the final hole for a 67, Austin shot 71, and Remesy 72.
It was an international leaderboard. Montgomerie is from Scotland, Toledo from Mexico, Kuramoto from Japan, Remesy from France, and Fowler from Australia.
The round began with temperatures in the upper 40s, like the first round Thursday. The sun lifted it into the mid-70s, although a tricky wind made scoring difficult.