Scott Piercy and Marcus Fraser carded six-under rounds of 66 to take the first-round lead at the WGC-Cadillac Championship, upstaging the world's top three.

Only a bogey at the 18th at Trump National Doral cost Piercy an even better round in Miami, Florida, while Fraser holed seven birdies in his impressive start.

The pair are a shot clear of American 2009 champion Phil Mickelson, who is outright third in what is a congested top part of the leaderboard.

Adam Scott, fresh from breaking his winless drought at The Honda Classic, is among four players who opened with 68s.

Scott made the dream start to his round with an eagle at the 10th, but he needed two late birdies to finish in a good position.

World number one Jordan Spieth, unable to impact on his past two starts, appears set to contend after carding a three-under 69.

Spieth mixed five birdies with two bogeys, including one at the ninth – his last.

The two players behind him in the rankings – Jason Day and Rory McIlroy – also made decent enough starts.

Day managed an even-par 72, while McIlroy, whose form has been questioned, produced a one-under 71 to be tied for 16th.

Unusually, Northern Irishman McIlroy's name was misspelt on his caddie's bib and the leaderboard.

He had appeared set for a better round than he managed, but a double-bogey at his final hole after his tee shot found the water proved costly.

Alongside Scott at four under are Englishman Danny Willett and American pair Charley Hoffman and Jason Dufner, while Spieth is joined by Jimmy Walker and Bubba Watson in a tie for eighth.

Defending champion Dustin Johnson endured an inconsistent round, settling for a 72.