Rory McIlroy kicked off golf's final major of the year with a superb five under par 67 to be only one off the lead at boiling hot Kiawah Island.
Fellow Irishmen Graeme McDowell and Padraig Harrington also got off to a solid start at the South Carolina track, posting four and two under respectively.
McIlroy's round put him on the heels of Carl Pettersson, the Swede, who posted six under, became an American citizen earlier this year.
Pettersson, yet another member of the long putter brigade following the major victories by Keegan Bradley, Webb Simpson and Ernie Els in the past year, was also bogey-free as the thunderstorms of earlier in the week gave way to near perfect conditions - apart from the energy-sapping heat.
He is not a member of the European Tour and therefore has not collected points since the race started last August and to play for America he had to become a citizen by the time he was 18.
Dutchman Joost Luiten, who after an eagle and six birdies was clear of the field in his first major in the United States, bogeyed his last four holes - echoes of Adam Scott at The Open last month - and had to settle for a 68.
Tiger Woods was another early starter and kept himself in the hunt with a 69, while Ian Poulter - keen to boost his chances of qualifying automatically for the Ryder Cup as well as landing a first major - returned a 70.
Last year's Open champion Darren Clarke had a 73 that included just about everything from an eagle at the seventh to double bogey seven on the 11th. Michael Hoey was five over with three to play in round one.
McIlroy said: "I think that's my first bogey-free round in a while and it was a great way to start.
"I'm pretty comfortable on the course and only played nine holes on Monday and nine on Tuesday - I didn't feel I needed to play more.
"I'm expecting this to be the best day of the week (weather-wise), but it's hot and you just try to stay hydrated."
Harrington, speaking after his two under opening round, said: “I left a lot of shots out there. I was lucky with the shots I gained as I holed two long putts. Happy with the score but certainly could have done a lot better.
“I’m swinging the club well and I need to trust my putting and my short game better.”