PHIL MICKELSON CELEBRATED his 51st birthday on Wednesday by making final preparations for the US Open as the six-time major winner chases more golf history starting Thursday at Torrey Pines.

Mickelson became the oldest major champion last month with a shock victory at the PGA Championship. The left-hander will be the oldest in the field of 156 teeing off at the 7,652-yard, par-71 oceanside layout.

“It’s a unique opportunity because I’ve never won a US Open,” Mickelson said. “I have a chance to prepare properly and I wanted to put in the right work.

“I’ve shut off a lot of the other stuff to where I can kind of focus in on this week and really give it my best chance to try to play my best.”

Mickelson would complete a career Grand Slam by winning the US Open, joining a select group that includes Tiger Woods, Jack Nicklaus, Ben Hogan, Gary Player and Gene Sarazen.

But he has a history of heartbreak in the event with a record six runner-up finishes, most recently at Merion in 2013.

Mickelson, who grew up only a few miles from Torrey Pines, remains a popular bet at 50-1 odds after his historic triumph at Kiawah Island.

“To come into this event as the most recent major winner is special,” Mickelson said.

World number 30 Mickelson has won three US PGA events at Torrey Pines but none since a 2001 renovation.

That’s why he spent the past two weeks re-learning the details of a course he once knew like the back of his hand.

“I’ve played out here a bunch since the redo, but I really haven’t spent a lot of time to learn the nuances,” Mickelson said. “I put a lot of time in on the greens. I needed to kind of relearn and see the breaks and know what the ball does on these greens.”

Mickelson tees off on the 10th hole at 7:51 a.m. (1451 GMT) Thursday in a Southern California trio with Max Homa and fourth-ranked Xander Schauffele.

Fans won’t see a first-round group that features feuding rivals Brooks Koepka, a four-time major winner, and defending champion Bryson DeChambeau.

They were placed on opposite ends of the start list, Koepka in the fifth group off the 10th tee in the morning and DeChambeau in the fifth group off the first tee in the afternoon.

A video of Koepka showing his disdain for a loud-talking DeChambeau from last month’s PGA sparked the spat, which has extended into social media.

“I hope on the weekend we can play against each other and compete,” DeChambeau said. “It would be fun and would be great for the game.”

World number one Dustin Johnson, last year’s Masters champion, could be overtaken in the rankings if number two Justin Thomas or Spain’s third-ranked Jon Rahm win the US Open.

Johnson would need to finish worse than solo 17th if Thomas wins or worse than a two-way share of 18th if Rahm wins to be dethroned.

The US Open will be the final event to determine Tokyo Olympic berths, with the field to be based upon next week’s rankings.

- Plaque honors Tiger win -

A plaque recalling Woods winning the 2008 US Open on a broken leg was dedicated Wednesday on the 18th hole at Torrey Pines. Woods is absent after suffering severe leg injuries in a February car crash.

“He’s going to be sorely missed,” said US Golf Association chief executive officer Mike Davis. “All of us in the golf world, certainly the USGA, wish him a speedy recovery.

“I’ve had the chance to text back and forth a few times with him, and he seems like he’s in good spirits.”

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