Another big marquee group teeing off on the 10th.

Six-times runner-up Phil Mickelson is chasing the career Grand Slam... again. But at least this time he's got a bit of form behind him, having won the US PGA Championship last month.

Lefty is out with the driver. Into the first cut.

He's playing with Xander Schauffele - four US Open appearances, four top-six finishes - and he finds a fairway bunker off the tee.

The 11th is a 222-yard par three. Collin Morikawa tugs his tee shot left into the thick, thick rough. A hack out to 20 feet and the American looks set to drop a shot.

Justin Thomas is straighter, his ball trundling to the back edge of the green. He nudges his ball down the hill for another tap-in par.

Brooks Koepka has a birdie look from 18 feet but his effort slides three feet by.

Morikawa's par putt stays on the green. Bogey.

Collin Morikawa and Justin Thomas get a little greedy with their approach shots to the 10th green and pay the penalty as their balls fall fractionally short and plummet into the bunker protecting the flag.

Brooks Koepka, perhaps conscious of those efforts, finds the heart of the green and the ball spins back to around 25 feet.

Morikawa splashes out to four feet. Par. Thomas hits a sublime effort to tap-in range.

Koepka with a steady two-putt for par.

England's Marcus Armitage is agonisingly close to a birdie on the 12th hole, as his putt rolls just wide of the hole. He stays on par.

As does Ireland's Shane Lowry, who hits a decent chip and putt on the first.

You could easily confuse this year's US Open with an Eastenders episode, such is the level Bryson DeChambeau and Brooks Koepka's spat has reached in recent weeks.

The ongoing feud seemed to reach its zenith when Koepka posted a video on social media offering free beers to fans ejected from the Memorial Tournament for heckling DeChambeau.

The defending champion has just called it "banter" in a year when the PGA Tour has launched a $40m fund which will be split by 10 golfers to "recognise and reward players who positively move the needle" by generating coverage for the sport.

I guess we'll see if it adds a bit more fuel to the fire this weekend.

Image source, Getty Images

One of the early marquee groups is under way, playing from the 10th hole.

Collin Morikawa, the 2020 PGA champion is first off, booming a drive down the middle of the fairway.

Justin Thomas, 2017 PGA champion is next, and his ball dribbles in to the first cut.

Brooks Koepka, 2018 and 2019 PGA champion, and 2017 and 2018 US Open winner, is long and straight. Perfect.

There had been rumours - which Bryson DeChambeau denied - that he and Brooks Koepka had been asked to play together at Torrey Pines.

It turns out they have been separated.

Koepka is teeing off any moment with Justin Thomas and Collin Morikawa.

DeChambeau starts at 22:44, with Rory McIlroy and Justin Rose out at 23:06.

A full list of all Thursday and Friday's tee times is here (add 90 minutes to today's times due to the fog delay).

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Torrey Pines is a regular fixture on the US PGA tour having hosted the Farmers Insurance Open since 1968, with Patrick Reed claiming a five-shot win at the end of January.

The American is in the same group as Australia's Marc Leishman and Spain's Jon Rahm, who held a six-shot lead at the end of the third round at the Memorial Tournament earlier this month.

But the world number three had to withdraw after being told he had tested positive for Covid-19 as he walked off the 18th green. The next day Patrick Cantlay won in a play-off with Collin Morikawa, the US PGA winner in 2020.

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England's Marcus Armitage shot a seven-under-par 65 to claim his first European Tour title at the European Open in Hamburg. But that only tells half the story.

It was a first win on the European Tour at the 71st attempt for Armitage, and the victory earned him a place at Torrey Pines this week in what will be just his second appearance at a major.

After wins on the EuroPro Tour and the Challenge Tour and struggles just to retain his European Tour card, Armitage was holding back the tears after that win in Hamburg. I'll certainly be rooting for the 33-year-old, who's just claimed par on his first hole.

"I'm an emotional guy, I'm struggling to keep a lid on it here," he said. "Twenty years ago I lost my mum and I've dreamt about this since that day, being a winner, and you have days where you think it might not happen but I just stuck at it.

"Today is a great day and I'm sure she would be proud, and everybody in my team that's helped me - this one's for me.

"All those days on my own dealing with life and I'm sure a lot of people do, all those lonely days on my own working on my dream and I think I've got to take a lot of credit for it myself."

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Here's a list of the big names out early today...

Starting on hole one

16:59 Francesco Molinari (Ita), Henrik Stenson (Swe), Shane Lowry (Ire)

17:10 Matt Fitzpatrick (Eng), Tyrrell Hatton (Eng), Viktor Hovland (Nor)

17:21 Martin Kaymer (Ger), Webb Simpson (US), Gary Woodland (US)

Starting on hole 10

16:48 Matthew Wolff (US), Brian Harman (US), Tommy Fleetwood (Eng)

16:59 Justin Thomas (US), Collin Morikawa (US), Brooks Koepka (US)

17:10 Matt Kuchar (US), Kevin Kisner (US), Billy Horschel (US)

17:21 Xander Schauffele (US), Phil Mickelson (US), Max Homa (US)

After Phil Mickelson ended his major drought, can Rory McIlroy follow suit?

The Northern Irishman, 32, has not won one of golf's biggest four titles since claiming his fourth major in 2014 and has had 12 top-10 finishes in majors since.

Slow starts have been an issue - over all majors since the start of 2015, he has been a cumulative 35 over par.

"It's a matter of freewheeling from the Thursday and not the Friday," he said. "It's about playing as free as I can."

When asked to explain his first-round struggles, the world number 11 replied: "[I'm] probably just putting a little too much pressure on myself, playing too carefully, being a little tentative.

"If I went out and played this golf course any other week, [I'd] play free, and it's just the same thing. You just have to be able to swing with that freedom, and that's sort of what I'm trying to get back to.

"There's no surprise that if I do have, say, not a great first day that I'm able to play well the rest of the tournament because that does free you up. It's like, OK, well, the bad one's out of the way, and now I can just sort of freewheel."

Image source, EPA

And we're under way, the fog has cleared enough for the first group, including Italy's Edoardo Molinari, to tee off at Torrey Pines.

Already heard 'marine layer' several times today. That's something I don't remember hearing about in GCSE Geography!

Phil Mickelson spent four days defying those waiting for him to capitulate to win the US PGA Championship at Kiawah Island last month for his first major in eight years.

A day after turning 51, the American left-hander begins his quest for the one major he has yet to win. He does so at Torrey Pines in his home city of San Diego - the anticipated script could not be better.

Despite winning the most recent major, the bookies view him as only a 50-1 shot, but the dream of becoming only the sixth man to complete the full set of golf's biggest prizes is very much alive.

Mickelson has been runner-up in America's national championship on six occasions and finished joint 18th the last time it was held at Torrey Pines in 2008.

Image source, Reuters

Tiger Woods is one of only five men who have managed to win all four majors. Here they are and the year they completed a career Grand Slam:

• Gene Sarazen (1935)
• Ben Hogan (1953)
• Gary Player (1965)
• Jack Nicklaus (1966)
• Tiger Woods (2000)

That was Tiger Woods' last major win before pulling off an unexpected triumph at the Masters in 2019, and Phil Mickelson ended his own major drought by winning the US PGA Championship last month.

That saw him become the oldest player to win a major and fuelled hopes that he can, at long last, complete the career Grand Slam at this week's US Open. Plus, he's playing just down the road from his San Diego home.

The spectacular cliff-top course knows how to stage great golfing stories and were Mickelson to land successive major titles at such an advanced age it could boast another extraordinary tale.

"It's a unique opportunity," he said. "It's in my backyard. I have a chance to prepare properly, and I wanted to put in the right work.

"So I've shut off all the noise. I've shut off my phone. I've shut off a lot of the other stuff so I can focus in on this week and give it my best chance to try to play my best."

Image source, Reuters

The US Open has been held once before at Torrey Pines and the San Diego course is best remembered for Tiger Woods' epic triumph in June 2008, when he defied the pain of knee ligament damage and stress fractures to beat Rocco Mediate over 91 holes.

Woods holed a 12-footer for birdie on the 72nd hole to force a play-off between the American pair, which would be played on the Monday over 18 holes. Then on the 18th on Monday, Woods sank another high-pressure birdie putt to take it to a sudden-death extra hole, on which he finally managed to clinch a famous victory.

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So the South Course is 7,652 yards long, and will have some testing hole locations for the first round.

The South Course is a whopping 7,652 yards long and is a par 71 (35-36). And the changeable weather adds to the unpredictability...

Play has been delayed further in San Diego. Should now be a 16:15 BST start.

And this is why the US Open is one of the toughest tests in golf. Not only is Torrey Pines' South Course the longest layout on the PGA Tour rota, but it's right on the Pacific Ocean. And today's start has been delayed to 15:45 BST due to fog.