TROON, Scotland — John Cook of the United States took a one-stroke lead in the Senior British Open today, shooting a 4-under 67 to capitalize on Bruce Vaughan's midround collapse.

Vaughan was 7 under and three shots clear after a birdie on No. 8 at Royal Troon, but the American then bogeyed four holes in a row around the turn. Cook rolled in a 4-foot birdie at the 13th en route to a 6-under 207 total after the third round.

Vaughan had a birdie at the last for a 69 and second place, one stroke ahead of Eduardo Romero (68) of Argentina.

Tom Watson (71) and Bernhard Langer (71) were at 212, while Greg Norman, who shot a bogey-free 67, was seven shots back from Cook and tied for sixth.