The world number six finished on eight under par, having started brilliantly with four birdies from the first four holes.

A single bogey came at hole seven, before he recorded a further five birdies.

Fellow American Rickie Fowler finished the front nine on three under par, including a bogey on the ninth, and would eventually finish six under par.

World number 51 Brendon Todd had a great back nine to go level with Fowler on six under, birdieing five of his last nine holes.

South Korea's Kang Sung-hoon had similar success on the last seven holes, recording four birdies to finish fourth on five under par, three strokes off the lead

Americans Matt Kuchar, Chez Reavie, Max Homa and Justin Thomas all finished the day on four under par.

New world number one Jon Rahm of Spain had a difficult day, sitting in joint 36th on even par after an inconsistent round. 

The man he replaced, Rory McIlroy, has a lot of work to do to, finishing a disappointing three-over round with a total of five bogies.

Other high-ranked strugglers included world number 10 Patrick Cantlay - also on three over par - and England's Tommy Fleetwood, who is currently on two over.

World numbers four and five Webb Simpson and Dustin Johnson are seven shots behind the leader on one under par.