FIRST ROUND LEADERBOARD US unless stated -9 P Mickelson -8 G Coles (Aus) -7 C Warren -6 J Durant, I Poulter (Eng), S Parel Selected others: -5 D Howell (Eng) -4 P Harrington (Ire), L Donald (Eng) -3 R Goosen (SA) +1 G McDowell (NI) +2 J Rose (Eng)

Mickelson equalled the course record with birdies at six of his first seven holes and at three of his last five.

Australian Gavin Coles had earlier shot his lowest-ever score on the US Tour with a 64.

England's Ian Poulter forced his way onto the leaderboard late on but bogeyed the 17th to slip to six under.

It was a good recovery from Poulter, who failed to qualify for next week's Masters after finishing in a tie for 27th place at last week's Players Championship at Sawgrass.

"Maybe I've been pressing too hard for the Masters and today I just played golf," he said. "I wasn't getting frustrated and shot 66 like it's a breeze."

David Howell is also in contention for a first victory in America after a 67, while Luke Donald and Padraig Harrington, paired together, came in with 68s.

Mickelson's start could have been even more spectacular. He missed 14-footers on the third and fourth, one for birdie and the other for eagle.

He suffered a setback when he three-putted the eighth, but he came back with putts of 20 and four feet on the 11th and 14th.

Poulter's charge included an 18-footer from off the ninth green for the first of four successive birdies, while Howell, the current European tour number one, had seven birdies.

The highlight of Harrington's round was a 56-feet putt for eagle at the 18th, his ninth hole of the day.