Andy Zhang tees off on the first hole during a practice round for the 2012 U.S. Open golf tournament on the Lake Course at the Olympic Club in San Francisco. At 14, Zhang is the youngest player ever to be admitted to the field. (JEFF HAYNES / REUTERS)

Before this week, Andy Zhang’s U.S. Open experience was precocious enough. At 14, he had made it through local qualifying and played well in the next stage, a sectional qualifier, barely missing out an unlikely berth in the national championship. Born in China but groomed at David Ledbetter’s academy in Florida, Zhang seemed poised for future success at future U.S. Opens.

And then, Monday night, England’s Paul Casey withdrew with an injury, and Zhang was on the receiving end of a historic phone call: He had gained entrance into the Open as an alternate, becoming the youngest player ever to play the event.

“Of course I’ll be nervous,” Zhang said. “Look at all these great champions I’ll be walking alongside. Who wouldn’t be nervous? But it is also going to be great.”

Zhang flew from Florida on Monday night, and arrived on the range a bit overwhelmed. At 6 feet and 185 pounds, he looks older than his age — until he smiles, revealing a mouth full of braces. His first move upon arriving at the Olympic Club: Sign up for a practice round. His choice: Masters champion Bubba Watson, who played with his good friend Aaron Baddeley of Australia.

“It was fun getting to meet him and watching a talent like that,” Watson said. “He’s a big boy for 14, and he can hit it good. Obviously at 14, he’s got a lot of growing up to do with his game.”

At the other end of the spectrum: 53-year-old Michael Allen, a Champions Tour player who qualified to play at his home course. Allen has been a member at Olympic since he was 14.

“I’m baffled,” Allen said when he heard about Zhang’s qualification. “I can’t imagine. I wouldn’t let my 14-year-old kid go backpacking over the weekend.”

Zhang will play with Japan’s Hiroyuki Fujita and American Mark Wilson on Thursday and Friday. Jordan Spieth, an amateur who plays at the University of Texas, gained entry as the first alternate when Brandt Snedeker pulled out with a rib injury.

McIlroy’s pitch

Rory McIlroy was set to commemorate his 2011 U.S. Open title by throwing out the first pitch at Tuesday night’s San Francisco Giants game. The Northern Irishman admitted to having scant familiarity with throwing a baseball. “I don’t know whether to play it conservatively and just lob it into his hand or go for the fast one,” McIlroy said.

He also was honored with a bobblehead issued in his likeness.

“I think it’s maybe better looking than me, which is a good thing,” he said. . . .

Mike Davis, the U.S. Golf Association’s executive director, reaffirmed the governing body’s commitment to holding an 18-hole playoff on the Monday after the U.S. Open should there be a tie.

“It’s not necessarily real convenient for television or the on-site spectators or vendors or even the officials,” Davis said, “I do think when it’s all said and done that we believe that this week is more than just entertainment. This is about determining a national champion.”