Updated

Tom Watson took advantage of an early tee time to shoot a 4-under 66 and earn the clubhouse lead in the opening round of the U.S. Senior Open on Thursday.

With the temperature expected to soar to 104 degrees in the afternoon, Watson worked through Del Paso Country Club before the scorching heat in California's capital city intensified. The eight-time major champion overcame a double bogey before the turn and had four birdies in his final nine holes.

Michael Allen and Lee Janzen each finished at 67.

Defending U.S. Senior Open champion Colin Montgomerie and Champions Tour stalwart Bernhard Langer were among those teeing off in the afternoon. Montgomerie and Langer have combined to win six of the last seven senior majors.