US Open 2017: England's Paul Casey one off Rickie Fowler's first-round lead at Erin Hills

England's Paul Casey trails American Rickie Fowler by one shot after round one of the US Open at Erin Hills.

Casey is joint second with Xander Schauffele but they were eclipsed by Fowler whose seven-under 65 equalled the lowest US Open first-round score.

England's Tommy Fleetwood is tied for fourth on five under with Brooks Koepka and Brian Harman, while Lee Westwood and Andrew Johnston are three under.

Defending champion Dustin Johnson is three over; Rory McIlroy is six over.

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World's best struggle

None of the world's top-six golfers posted an under-par score on a day when a US Open first-round record 44 players managed to do so after heavy rain earlier in the week softened the greens and made the fairways more forgiving.

World number three Jason Day had the worst round, signing for two triple bogeys in a seven-over 79, while Japan's Hideki Matsuyama and Sweden's Open champion Henrik Stenson both finished on two over, one adrift of Jordan Spieth.

McIlroy, the 2011 champion, was returning after a month out with a rib injury and his round started in perfect fashion with an eagle-two on the par-four second after driving the green.

However a bogey followed at the third and he had two double bogeys on his back nine after hitting his ball into the thigh-deep fescue rough.

Prior to the tournament, the 28-year-old Northern Irishman had defended the severity of the rough, saying the fairways were "the widest played at a US Open" and "if we can't hit within that avenue, you might as well pack your bags and go home".

After his round, McIlroy, who hit just five fairways to tie for last in the 156-man field in that category, said: "I don't think I hit a fairway from the 10th and you cannot play this golf course if you are not in position off the tee.

"It was just one of those days. My timing was just a little bit off. I started missing some left and tried to correct it and missed a couple right."

Casey cuts Fowler's lead

Fowler's round, on the longest course in major championship history at 7,845 yards, equalled the record seven under totals posted by Jack Nicklaus and Tom Weiskopf, who both shot 63 in the first round on the par-70 layout at Baltusrol in 1980.

He was among the early starters and knocked in three birdies on the front nine and four on the back to set a clubhouse lead that nobody really threatened.

However, the 28-year-old, who is yet to win one of golf's four majors but has finished in the top five at them all, said: "I'd rather be remembered for something that's done on Sunday.

"I didn't see seven under at the start of the week, but today is the best we are going to get. I just kept making putts when it mattered."

Casey's best finish at a US Open is tied 10th at Oakmont in 2007

Casey came closest to joining him atop the leaderboard. He chipped in from 30 yards to eagle the first and he birdied three more holes on the front nine to turn at four under par.

After a bogey on the 10th, his second of the round, Casey had three birdies in his closing eight holes to move within one of the lead.

"I'm ecstatic," said the 39-year-old. "I'm over the moon with a 66. I'm feeling really, really good about this golf course. I like classic US Open courses but this is different. It has an Open Championship feel about it."

Schauffele, like his compatriot Fowler, had a bogey-free round. He had a chance to tie the lead but missed a 14-foot birdie putt on his last hole.

Fleetwood, who has missed the cut in six of his previous seven major appearances [he finished 27th at the 2015 US Open], said: "The course was as receptive as it's going to be but I never really tried to make a birdie, they just seemed to happen along the way.

"You don't really think about shooting five under at the US Open. Seven under is ridiculous."

Spieth's putting woes

Johnson and Spieth both struggled with their putters on the opening day in Wisconsin

World number one Johnson started on the 10th and had two bogeys, one double bogey and a birdie in four holes from the 14th. He parred the other 14 holes to start the defence of his US Open title with a three-over 75.

Johnson was playing with Germany's 2014 winner Martin Kaymer, who finished level par, and 2015 champion Spieth, who shot one over.

Spieth joked that he and Johnson "might have a pillow fight putting contest" after holing just one of "15 makeable birdie putts".

The 23-year-old added: "I hit the ball phenomenally, just didn't make anything. I missed one fairway , which is the best driving round that I've had maybe in my life.

"Once you get through six or seven misses the hole starts to look smaller and smaller. It just looked like I was putting at half a cup. Sometimes it looks like I'm putting to two cups."

Those in contention

Kevin Na had been critical of the rough earlier in the week but the American had no complaints as he signed for a four-under 68, to sit alongside compatriot Patrick Reed, Australian Marc Leishman and Canada's Adam Hadwin who tied the US Open record for most consecutive birdies when he rolled in a sixth on the fifth hole, his 14th.

Garcia finished has had five top-10 finishes at the US Open and was tied fifth at last year's tournament

Masters champion Sergio Garcia eagled the first but was unable to capitalise on his strong start and needed two birdies in his last four holes to get back to two under. South Africa's Ernie Els dropped his only shots of the day on the par-four 17th and par-five 18th as the 1994 and 97 champion also opened with a 70.

There are a total of 44 players under par - the most ever at a US Open after round one, beating the 39 at Medinah in 1990. However, none of the top 17 on the leaderboard have won a major.

Among them are South Korea's 21-year-old Si Woo Kim, who last month became the youngest player to win the Players Championship. He is three under after a round featuring five birdies and two bogeys.

The best (and worst) of the Brits

English pair Westwood and Johnston ended tied for 11th but their paths were very different.

Westwood's quest to win a major at the 77th attempt got off to a solid start in benign conditions

The former overcame a double bogey on the 12th, his third hole, to reach the turn in three under and then parred his way in, while Johnston mixed six birdies with three bogeys. Compatriot Matt Fitzpatrick had seven birdies in his round but a double-bogey seven checked his progress as he posted a 70.

Justin Rose said he had to "grind" his way round the course. The Olympic champion, who won this title in 2013, was one under playing the last but missed a 10-foot birdie putt and took two more to finish with a bogey and level-par 72.

Richie Ramsey looked destined to be the best Scot but he double-bogeyed the par-three ninth, his last hole, to finish one over.

Martin Laird posted a level-par 72, while fellow Scotsman Russell Knox finished one over and Wales' Bradley Dredge is two over.

England's Danny Willett, who won the 2016 Masters, birdied the par-three ninth, his last hole, but signed for a nine-over-par 81, the joint second worst score of the day.

He joked on social media that the birdie "kept me in with a sniff".