SECOND ROUND LEADERBOARD US unless stated -16 P Mickelson -10 JJ Henry -9 JM Olazabal (Spa) -8 G Coles (Aus) Selected others: -6 I Poulter (Eng), L Donald (Eng) -5 D Howell (Eng), P Harrington (Ire) +3 G McDowell (NI) +8 J Rose (Eng)

The defending champion, who had a bogey-free second round with seven birdies, leads compatriot JJ Henry by six strokes.

Two-time Masters champion Jose-Maria Olazabal was also in great form, shooting a 64 to lie on nine under.

England's Ian Poulter shot a level-par round and is 10 shots behind Mickelson.

After his 65 on Thursday, Mickelson was straight back into the groove, holing 13-foot birdie putts at the first two holes.

"I enjoyed coming out this morning when the greens were fresh and making a couple of putts early on," said the 40-year-old left-hander.

"I don't think I go into any round expecting to shoot 63 or 65. But when you're playing well and you have some confidence, if you just get a couple of putts to go in, it sets the tone for the day."

It's going to be difficult for anybody to catch Phil Mickelson unless we play some really awesome golf on at the weekend Jose-Maria Olazabal

Olazabal, who had a 71 in his opening round, said putting was the key to his impressive score.

"The only area where I was not all that good was the driving. Even though I hit most of the fairways, I did not feel comfortable with it," said the Spaniard.

But Olazabal, who was one of four players edged out by Mickelson in a play-off for last year's title, admitted that the American would be hard to overhaul now.

"It's going to be difficult for anybody to catch him unless we play some really awesome golf on at the weekend."

Ireland's Padraig Harrington climbed into a tie for sixth place on six under only to crash to a quadruple bogey eight on the 434-yard 12th.

But he recovered with three late birdies for a 71 to lie on five under alongside David Howell.