Bernhard Langer and Jeff Maggert lead US Senior Open.

A bogey apiece on the final hole from co-leaders Bernhard Langer and Jeff Maggert kept the chasing pack within one shot after the third round of the US Senior Open.

Dropped shots at 18 from German Langer and American Maggert left them with a one-stroke lead over a group of eight, including history-chasing Tom Watson, who at 65 is trying to become the oldest major winner in Champions Tour history.

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Defending champion Colin Montgomerie is also one stroke behind, while Spaniard Miguel Angel Jimenez is among another large group two back.

The final-hole drama means that 16 players lie within two shots of the lead on a jam-packed leaderboard at Del Paso Country Club in Sacramento, California.

Langer and Maggert are at five-under 205.

Watson struggled on the front nine with a two-over 38, but closed with a tidy back nine for a one-over par 71, including an excellent par-saving putt at 18.

"It's like a horse race," Watson said. "Right now I'm a length behind. Let's see what we can do in the stretch."

Maggert, who fired an even-par 70, won the season's first senior major, The Tradition.

Langer, 68, who won the Senior Players Championship only two weeks ago, is trying to win for the fourth time in the last seven senior majors.

"It's too bad I finished with a bogey," Langer said. "I didn't mean to."