SAN FRANCISCO -- Michael Thompson remains the clubhouse leader at the U.S. Open, firing a 4-under-par 66 at Olympic Club in San Francisco.

Tiger Woods and David Toms each shot 1-under 69s, the only other completed rounds under par with about half the field still on the course.

Phil Mickelson opened with a 76 and reigning Masters champ Bubba Watson shot a 78.

The Associated Press