Jeff Maggert and Peter Fowler have taken a one-stroke early lead over the bunched field midway through the second round of the U.S. Senior Open.

Maggert shot a 65, and Fowler finished at 66 to move to 5 under on Friday at the Del Paso Country Club, where the temperature was expected to rise above 100 degrees for the second straight day.

Defending champion Colin Montgomerie shot another 68 and was among those one stroke back. Champions Tour stalwart Bernhard Langer had a 66 to move to 3 under.

Montgomerie and Langer have combined to win six of the last seven senior majors.

Tom Watson, who shot an opening-round 66, was teeing off in the afternoon heat. The 65-year-old became the oldest first-round leader in U.S. Senior Open history.