He shot a bogey free round to top the standings after his 18 holes
Defending champion Jordan Spieth set an early clubhouse lead on day one of the US Masters golf.
The American signed off on a round of 66, leaving him 6-under par, although Ireland's Shane Lowry and World No 1 Jason Day were closing in fast as he finished.
The 22-year-old is looking for his third major title.
The World No 2 told Sky Sports News, getting round without dropping a shot was a big bonus.
"In order to stay bogey free, which isn't necessarily a goal, the goal is to try an shoot under-par each day. It's going to take a little bit more in the ball striking and the patience that we had today," he said.