Taking advantage of cool morning conditions and mostly avoiding the canopy of trees engulfing Sahalee Country Club in Sammamish, Wash., Bruce Vaughan opened with a 4-under 66 on Thursday to take a 2-stroke lead in the U.S. Senior Open.

The 2008 Senior British Open champion — his only victory on the Champions Tour — made just two bogeys in a steady round, while favorites such as Fred Couples and Tom Watson were far more shaky.

"It's just the first day. I mean, there is a lot of golf left and a lot of trouble out there for the next three days," Vaughan said.

Loren Roberts and amateur Tim Jackson, the leader a year ago after two rounds, shot 68s. Bernhard Langer, the British Senior Open winner Sunday, and Tom Lehman were another stroke back along with Mark Calcavecchia, Joe Ozaki and Michael Allen. Couples, the hometown favorite, and Watson opened with 70s.

Other favorites were far off the leaderboard. Defending champ Fred Funk shot 76. U.S. Ryder Cup captain Corey Pavin needed a birdie on his final hole to shoot 72.

Tseng, Hull tied for lead at Women's British Open — Taiwan's Yani Tseng and Australia's Katherine Hull shot 4-under 68s to share the first-round lead in the Women's British Open.

Tseng, the Kraft Nabisco winner in April for her second major title, finished her bogey-free round at Royal Birkdale with a birdie and an eagle.

Brittany Lincicome, Anne-Lise Caudal, Amy Yang and Sun Young Yoo opened with 69s, and Michelle Wie and In-Kyung Kim shot 70s. Hall of Famer Juli Inkster and top-ranked Jiyai Shin, the Evian Masters winner last week in France, topped a group at 71.

Howell leads at Irish Open — England's David Howell shot a 7-under 64 to take a 1-stroke lead in the Irish Open. Ireland's Damien McGrane and England's David Howell opened with 65s. England's Robert Rock was disqualified for signing an incorrect scorecard — his scores on the 14th and 15th holes were transposed — after shooting a 65.