Koepka, who if he was to go on and win this week will have won four of his last seven major championships, played late in round one and made the turn in 1 under before birdies at the 10th, 12th, 13th, 14th and 15th swept him to a two-shot lead before De Chambeau birdied his last four holes to join Koepka in the lead.
Koepka had a chance to take the outright first-round lead with a ten-foot birdie putt at the last but he would miss although his opening round of 66 would better his previous best day one score by 7 shots.
De Chambeau's round was by five shots the best of the now nine competitive rounds he has produced at the Masters so both have made significantly better starts than has been the case in the past and it augurs well for what lies ahead.
Phil Mickelson is one shot from the lead and on his own in 3rd place after he birdied five of his last seven holes for a round of 67.
DeChambeau rolls in another birdie - Getty Images / European Tour
Adam Scott leads the Australians in a share of 6th place, the 2013 champion reeling off three birdies in his last four holes to share the then lead but the eventual leaders, out later in the day, would rush past Scott and several others at 3 under par 69.
Scott’s fellow Queenslanders, Cameron Smith and Jason Day, are just one shot behind Scott in a share of 11th place after Smith, too, finished strongly with two late birdies to finish with 2 under 70.
Scott has often been burdened with slow starts to his major appearances but after an early bogey at the demanding 7th hole, Scott birdied the 8th and 9th (the latter of which was from the pine straw) to make the turn under par.
A bogey at the 12th had him back in the pack but a two-putt birdie from 22 feet at the 15th, a 14- footer at the 17th and a 14-footer at the last saw him take a share of the lead in mid-afternoon.
Scott’s mid-morning tee time resulted in cool, soft conditions and a very long golf course, especially early on in his round, but once the bogey at the 7th was behind him he would add five birdies and the bogey at the 12th for an impressive start to his 18th appearance at Augusta National.
The effort equalled Scott’s best opening round at the Masters having also recorded 69 on day one in 2010, 2013 and 2014.
Smith is playing in just his third Masters having made the cut on both previous occasions and finished a very impressive 5th in 2018. His increasing knowledge of one of the more complex golf courses in major championship golf has seen him play his last 54 competitive holes at Augusta National in 10 under par.
Like Scott, Smith was slow out of the blocks, a bogey at the 1st after finding the fairway bunker from the tee before birdies at the 7th and 8th had him back on track.
Jason Day was once again plagued by an injury for much of his round, a re-occurrence of his on-going back problems seeing him struggle throughout his round and stopping for assistance on occasions. He was still able to produce a fine round of 70, however, fighting off an opening hole bogey with a series of birdies before a bogey at the 17th.
It was a remarkable round especially considering that at various stages it appeared as if he might well have been forced to withdraw.
Marc Leishman, too, would bogey the 1st but he made the run in 1 under before a double bogey at the 10th after mud on his ball caused a wayward approach. He would, though, finish with 72 and importantly is just six shots from the lead in what is an extremely congested leader-board given that at even par he is in 29th place.
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