Kuchar clings to US Open lead as Mickelson lurks
Matt Kuchar of the United States hits his tee shot on the second hole during the first round of the 114th US Open on June 12, 2014 in Pinehurst, North Carolina - by Mike Ehrmann
Early starters took advantage of moist conditions on the turtle-backed greens, but as the sun rose higher so too did temperatures, green speeds and scores.
Kuchar opened and closed the front nine with birdies and added another at the par-5 fifth to stand on three-under with three holes to play with Fitzpatrick, 2010 US Open champion Graeme McDowell and Korean-born American Kevin Na one stroke adrift.
Fitzpatrick, the 19-year-old reigning US Amateur champion who plans to turn professional next week at the Irish Open, opened with birdies at the 10th and 12th. The Englishman stumbled with back-to-back bogeys at 14 and 15 before birdies at 16 and the second.
Na sandwiched birdies at 13 and 15 around a bogey and took another bogey at the second but rebounded with a chip-in eagle from 35 feet at the par-5 fifth.
Northern Ireland's McDowell eagled the fifth as well, having also taken a bogey at the fourth and a birdie at 14.
Reigning British Open champion Mickelson, a six-time US Open runner-up trying to complete a career grand slam with a triumph, was in a pack on one-under.
The US left-hander, who turns 44 on Monday, opened with a four-foot birdie putt at the par-5 10th. He birdied the 14th but took a bogey at 15th and parred the next seven holes.
Mickelson would join Jack Nicklaus, Tiger Woods, Ben Hogan, Gary Player and Gene Sarazen in having won all four major titles with a victory.
"If I can manage my game and play it smart and just focus on the shot at hand, I feel like I'll give myself a good chance," Mickelson said.
Sweden's Henrik Stenson, US 20-year-old Masters runner-up Jordan Spieth, young US star Rickie Fowler and Germany's Marcel Siem were among the others on one-under.
Afternoon starters are topped by a powerhouse group that features world number one Adam Scott, reigning Masters champion Bubba Watson and 2011 Masters winner Charl Schwartzel of South Africa.
Fowler wore knickerbockers in a tribute to the late Payne Stewart, the 1999 US Open winner at Pinehurst who used them as a trademark.
Fowler opened with 10 pars before a birdie at the second.
Spieth opened with a birdie at the par-5 10th, birdied 13, took a bogey at 15 before making birdie at 16 and taking a bogey at the second.