Woods, Mickelson out early as US Open starts
The first group to set off at 7:00 am (1400 GMT) in cool, calm conditions was made up of the US trio of Shane Bertsch, Martin Flores and Tommy Biershenk.
All the anticipation was at the ninth tee, where the day's marquee grouping of Tiger Woods, Phil Mickelson and Bubba Watson set off 18 minutes later.
Woods was out to win a first major title in four years and thus bring his career haul to 15, just three shy of the all-time record of 18 set by Jack Nicklaus at the 1986 Masters.
Mickelson was bent on busting a US Open jinx that has seen him finish runner-up an unprecedented five times, most recently at Bethpage Black on Long Island in 2009.
For Watson, the challenge was to win back-to-back majors, having won in a playoff to lift The Masters at Augusta National in April.
In what looked like one of the most open US Opens in years, there were various other sub-plots.
World No.1 Luke Donald, and No.3 Lee Westwood were both gunning to become the first Englishman to win a major since Nick Faldo at the 1996 Masters, while a raft of young Americans like Matt Kuchar, Hunter Mahan, Rickie Fowler and Dustin Johnson hoped to follow the major example set by countryman Watson.
And then there was the arrival of Andy Zhang, a 14-year-old, born in Beijing and now living and studying in Florida, who at 14 and 1/2 years is believed to be the youngest golfer in US Open history, and a second US Open appearance for disabled golfer Casey Martin, who needs a golf cart to allow him to complete all 18 holes.
Adding to the uncertainty was the "quirky" nature of the Olympic Club's Lake Course, a 7,170-yard, par-70 layout, located on the Pacific Ocean side of the San Francisco peninsula, just south of the Golden Gate Bridge and built in 1927 on the eastern end of a giant sand dune.
The rolling course has what many see as the toughest six opening holes in major history and, in the 670-yard long par-five 16th, the longest hole ever to be played in the US Open.
Executive Director of the US Golf Association Mike Davis said that the course was a perfect theatre for US Open golf with a premium on players being able to shape their shots either way to allow for the sloping fairways and tight greens.
"This course more than any other US Open course we go to requires shaping and working the ball both ways, left-to-right and right-to-left - you get a real advantage," he said.
"And that's something we don't see as much anymore in today's game. It's more than just about hitting it long and hitting it straight."
McIlroy, who will play alongside Donald and Westwood in the day's other top draw, won by eight strokes last year at Congressional in Washington DC as his march to the world No.1 spot gathered pace.
He has struggled of late with three missed cuts in a row, but rediscovered some of his old form last week at the St Jude Classic in Memphis and believes he has the ability to match Strange and successfully defend his title.
"Life has changed over the past 12 months, but I'm just concentrating on listening to the people I trust around me and believing that I have enough ability and know-how to get through the bad patches," the 23-year-old Ulsterman said.
"I'm just glad that my bad spell didn't go on too long and I'm now back to something like my usual game - I have lots of positives to take into this week."
"I feel like I have a chance in these tournaments every time I tee it up."