Patrick Reed took a three-shot lead into the back nine as he went in search of a first Major Championship at the Masters Tournament.
The American played the front nine in level par at Augusta National to stay at 14 under, with Jordan Spieth emerging as his closest challenger after six birdies in his first 12 holes.
Rory McIlroy - who began the day closest to Reed as he goes for the career grand slam - was then at ten under alongside Jon Rahm and Rickie Fowler.
The leading pair showed signs of nerves off the first tee, with Reed sending his tee-shot left and having his follow through impacted by a tree while McIlroy went a long way right but both ended up in the front-left bunker with their second.
Reed's shot from the sand found the very back of the green for a bogey and with McIlroy getting up and down, the lead was quickly down to two.
The Northern Irishman then produced a moment of sheer brilliance on the second, hitting his second from 197 yards to four feet and two-putting for a birdie, with Reed getting up and down from the sand for a par.
The lead was back to three on the next, however, as McIlroy dropped a shot after leaving his second short of the green and Reed made a birdie putt from the back fringe.
Four-time Major winner McIlroy hit straight back, with a tee-shot to three feet on the fourth giving him a birdie.
The duo continued to slug it out as McIlroy came up short of the fifth to drop a shot but Reed three-putted from a long way out on the next and the door was easing open to the field.
None more so than Spieth, who produced some dialled-in iron play for birdies on the first and fifth, sandwiching another gain on the second. He took advantage of the eighth and when he made another gain from 12 feet on the next, he had turned in 31.
Rahm took advantage of the second with two putts from 48 feet and put his approach to the short third to five feet. Another nice approach brought a gain on the seventh but he needed an excellent up-and-down to save par on the eighth.
Reed put an approach to tap-in range on the seventh and with McIlroy dropping a shot on the next after going right off the tee and failing to get up and down, the lead was four.
Spieth's quest for a second Green Jacket came apart at the 12th in 2016 but when he holed a 30-footer from the back fringe on Sunday, he was the nearest challenger after starting the day nine shots back.
Fowler had bogeyed the fifth but fought back by making the most of the eighth and hitting a stunning approach into the ninth.
Henrik Stenson and Dustin Johnson were seven under, a shot clear of Justin Rose, Tony Finau, Cameron Smith and Bubba Watson.
Charley Hoffman was also eight shots off the lead with the help of a hole-in-one on the 16th, the 20th in Masters history on that hole.
Paul Casey shared the clubhouse lead a shot back after a 65 where he threatened the course record before a bogey-bogey finish.