Australia's Jason Day and American Brendon Todd share lead with England's Justin Rose one behind
TPC Harding Park in San Francisco hosts rescheduled tournament from 6-9 August
United States' Brooks Koepka aims for third straight US PGA title
Leaders: -5 J Day (Aus), B Todd (US); -4 S Scheffler (US), M Kaymer (Ger), X Schauffele (US), B Cauley (US), Z Johnson (US), B Koepka (US), J Rose (Eng), B Steele (US), M Lorenzo-Vera (Fra)
Selected others: -3 T Lewis (Eng); -2 T Woods (US), S Lowry (Ire), B DeChambeau (US) P Casey (Eng); -1 D Johnson (US); E R McIlroy (NI), T Fleetwood (Eng); ;+1 J Thomas (US);
No spectators allowed due to Covid-19 restrictions
Listen to BBC Radio 5 Live Sports Extra commentary
Iain Carter
BBC Sport commentator
Bryson DeChambeau was so revved up for that drive. It was like watching a contestant in a long-drive competition. He was tensing his muscles, he was waggling his club - there was real intensity to just swing this as hard as possible.
That is such a stark change in the game of golf. It's always been a controlled force but that almost felt uncontrolled.
Another bogey for Spanish 2017 Masters champion Sergio Garcia - his third in the first six holes. He's three over.
He's in the same group as countryman Jon Rahm, who fails to save par by an inch or two. Two over for the world number two.
Phil Mickelson, the other member of the trio, remains at one under.
It seemed that Bryson DeChambeau leant on the driver using his foot and snapped the shaft. Great work.
It wasn't out of anger, and he can have it replaced.
We march on.
He's having a right chuckle about it.
Speaking to the course marshal to explain what happened, Bryson DeChambeau said: "That was weird. It's all those swings I put in!"
Iain Carter
BBC Sport commentator
Were he to have slammed it into the ground, he can't replace it. There's no evidence he's done that.
OK. So Bryson DeChambeau's driver head is broken after he smacked his tee-shot wayward on the sixth.
Now if it was out of anger then he will not have it replaced...
Just about to watch a replay.
We've not mentioned England's Tommy Fleetwood yet, so now we will.
The two-time major runner-up - resplendent in all white - plays a lovely shot to escape from the bunker on the left of the seventh green and find himself a few feet from the hole.
He's currently one under for his round.
Image source, ReutersA much better approach from Bryson DeChambeau on the sixth - a good birdie chance.
Jon Rahm eventually taps in for par on the fifth - he remains on one over.
California's very own Phil Mickelson, in Rahm's group, manages another par - the 50-year-old is currently one under.
Jon Rahm is having a 'mare. His second to the green on the par four fifth should have been a foregone conclusion but it flops on to the edge.
Very poor from the Spaniard. He's currently one over.
It's been par o'clock for world number seven Bryson DeChambeau - the fourth one in succession, but he has been putting well.
The American is one under after five.
Image source, EPAThere are 59 players within four shots of the leader Jason Day.
Competitive.
...that was just for a par for Rahm on the par five fourth. A hole where he perhaps should have picked a shot.
Image source, ReutersA British winner? Just imagine someone like Tyrrell Hatton - or Matthew Fitzpatrick, who is no longer 18 - striding up to the final green on Sunday with a two-shot lead having landed his penultimate shot six feet from the home.
Anyway, our golf correspondent Iain Carter has dared to dream.
Yeah... yeah... we know it'll be an American.
It's not exactly been an eye-catching start for former world number one Jon Rahm.
He's bogeyed the second to go one over but has half a chance to get back to evens on the fourth - he's about eight feet from the hole.
Image source, EPARickie Fowler - yet to win a major - misses out on an eagle on the fourth by one of his moustache whiskers.
But he does manage successive birdies and is now one under, having bogeyed the first.
Rory McIlroy shot a level par 70 in his opening round, with just one birdie after the turn.
"On our second nine - the front nine - I just didn't hit the fairways and from there, the way the pins were tucked, I was just trying to play it to the front of the green and two-putt from 40 feet and move on to the next hole," he said.
"I need to hit a few more fairways tomorrow to try to attack some pins and not leave myself four and five-footers for par all day.
"There were a few holes where the pin was on the right of the green and the wind was blowing right to left so it's hard to get yourself close to those.
"But the course was there for the taking today - Jason Day shot five under and there have been a few four unders. I feel like I could have been a few shots lower but I grounded it out. With how I hit it on the back nine, even par actually wasn't too bad."
Phil Mickelson is wearing a pair of full mirror aviators (he's already sported them this summer) - possibly to remind people of the forthcoming release of Top Gun 2.
He hasn't been too... maverick... with his golf so far. He's one under after three.
Image source, EPA
Image source, EPAEnglishman Tom Lewis, off the back of a stunning tied second at the St Jude, is three under for the championship after his 67.
That score was helped by a superb birdie on the 17th. Lewis, 29 - who became the first amateur to shoot a 65 or better at The Open, in 2011 - also managed tied 12 at last month's Rocket Mortgage Classic.
One to watch this weekend.
Zach Johnson finished with an 82 for 12 over par!!
"Wait a sec, Zach Johnson shot a 66 fella??!"
Ahhh...I should have stated that it was Zach J Johnson who went around Harding Park in 82. It's his second US PGA.
Two years ago he met the other Zach Johnson at the US PGA at Bellerive - that must have been hilarious!!
English former Masters winner Danny Willett found it tough going today, finishing on five over.