(Reuters) - Rory McIlroy was reliving his worst nightmare at the Masters after a horror start to Saturday's third round while Phil Mickelson was among a trio of players who shared the tournament lead.

McIlroy began the day in a tie for third but for the second consecutive year at Augusta National the Northern Irishman's game collapsed and he tumbled down a congested leaderboard.

Seven different players had a share of the lead at various stages during the round, traditionally known as Moving Day, but McIlroy's only move was backwards.

After starting the day one shot behind overnight leaders Fred Couples and Jason Dufner, McIlroy shot a six-over-par 42 on the front nine, including two double-bogeys.

It rekindled memories of last year when he held a four-shot lead at the start of the final day but closed with a nightmarish eight-over-par 80.

Saturday's awful start left the 22-year-old McIlroy eight shots behind three-times Masters winner Mickelson, 2010 British Open champion Louis Oosthuizen and American Matt Kuchar, who shared the lead at six under.

Sweden's Peter Hanson was fourth on five-under with five holes to play while Ireland's Padraig Harrington and in-form American Hunter Mahan went into the clubhouse at four-under after matching rounds of 68.

The ever popular Mickelson charged to a share of the lead around Amen Corner when he birdied the par-three 12th then eagled the par-five 13th as the huge gallery watching him erupted in applause as he chases a fourth green jacket.

WORST FINISH

A frustrated Tiger Woods failed to make up any ground on the leaders and was in danger of his worst finish at the Masters since he turned professional.

Needing to shoot a low score to get back into contention, the former world number one could only manage an even-par 72 to remain at three over.

He made a bright start, with birdies at the third and fourth holes, as the crowd let out a mighty roar that echoed through the pine trees but failed to make another birdie all day as his emotions started to boil over.

On the 13th tee, he slammed his club into the ground after hooking his drive into the banks of Rae's Creek. On the previous day, he kicked one of his irons after missing a green.

Certainly I'm frustrated at times and I apologize if I offended anybody by that, Woods said. But I've hit some bad shots and it's certainly frustrating at times not hitting the ball where you need to hit it.

Defending champion Charl Schwartzel was also left hoping for a last-day miracle after the South African shot a 75 to end the day at six over while world number one Luke Donald was a further shot back after also signing for a 75.

(Editing by Frank Pingue)