AUGUSTA, Georgia (Reuters) - Phil Mickelson blamed a bad "mental" day and a lack of tournament sharpness for a four-over-par 76 on Thursday that matched his worst opening round at the Masters.
Three-times winner Mickelson, playing in his 22nd Masters, posted a stunning pair of sevens on the day and finished eight strokes behind first-round leader Bill Haas, who topped a crowded leaderboard after a sunny day at Augusta National.
"It was just perfect all day and there was possibilities for low scores and I actually played well," said a disappointed Mickelson, 43. "I know it's hard to say that, but I actually played well and I just made a lot of little mental errors.
"I made a lot of little mistakes around the green, but I didn't hit anything unsolid. I hit them solid, I just misjudged the shot."
Mickelson started with six pars before taking a triple bogey seven at the par-four seventh, where he criss-crossed through the green after sending a flop shot firmly to the other side of the green and chipped back too strong the other way as his vaunted short-game touch deserted him.
"I just hit them too firm, both of them on seven," lamented the American, ranked fifth in the world.
Birdies at the 10th, where he sank a curling 50-foot birdie, and 13th holes, moved the big lefthander back to one over par and in position to salvage a decent round.
However, after a bogey at 14 Mickelson took his second seven at the par-five 15th, where he spun his short approach back off the front bank and into the pond on the way to a double-bogey.
"At 15, I eased into it. I hit it solid, (but) I hit it terribly easy. It was just mental mistakes like that, that I wasn't sharp," he said. "I made a lot of mistakes like that around the greens and just threw away a ton of shots."
Mickelson said he may be suffering from a lack of tournament sharpness after withdrawing from last month's Texas Open with a pulled abdominal muscle.
"I hit all those chips solid and flush, but I misjudged them. I was just off. I was really off today," said Mickelson, who claimed his fifth major title with last year's rousing victory at the British Open. "It was very disappointing.
"It wasn't the best day for me today. I've got a lot of work to do tomorrow just to make the cut."
(Editing by Steve Keating in Toronto)