Rory McIlroy refused to blame the pressure of chasing a career grand slam for a disappointing performance in the 83rd Masters.

McIlroy needs a victory at Augusta National to join Gene Sarazen, Ben Hogan, Gary Player, Jack Nicklaus and Tiger Woods in having won all four major championships.

But, while a 43-year-old Woods was doing battle for a fifth green jacket at the top of a star-studded leaderboard in the third round, McIlroy was putting the finishing touches to a second consecutive 71 to finish one under par.

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"It was just one of those weeks, just not quite had it," McIlroy said after an erratic round containing an eagle, four birdies and five bogeys.

"I have not read anything. I knew my game was good coming in here, I've not let any external pressure get to me. I know I can play this golf course, just this week I have not played it well enough."

The 29-year-old was eight shots off the lead as he signed his card, but low scores were the order of the day and the four-time major winner was certain to be too far back to mount a challenge on Sunday.

McIlroy got his round under way with a perfect drive and an approach to 25 feet but left his birdie putt inches short and then strangely opted to hit a three wood off the tee on the par-five second.

That meant he needed the same club for his approach from more than 300 yards and still came up 30 yards short of the green, from where he failed to get up and down for birdie.

A more aggressive approach looked set to pay dividends as McIlroy hit his drive to the edge of the green on the short third, but after a poor chip the four-time major winner lipped out for birdie.

McIlroy was also less than happy with his tee shot on the par-three fourth, but holed from 32 feet for an unlikely birdie, only to then drop shots on the sixth, seventh and ninth, where his approach plugged in the top of a greenside bunker.

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A birdie on the 10th was immediately cancelled out on the next and another bogey looked on the cards after his drive on the 13th clipped a tree - but after pitching out on to the fairway McIlroy hit his approach to 13 feet and holed for birdie.

An eagle on the 15th and a birdie on the 16th kept McIlroy's faint hopes alive, but he then bogeyed the 18th after finding sand off the tee and with his approach.

A rain-softened course was expected to play into McIlroy's hands, but the 29-year-old added: "I don't think this course plays easier when it's soft.

"You get mud balls - I got a couple of flyers off the fairway - and when your iron play has to be its most precise of the year, to have mud balls is really tricky.

"I've just been making too many mistakes. I've been making the birdies and doing the things that you need to do around here. If I've missed a green I haven't got it up and down or put myself out of position."

Woods, seeking a first major title since 2008 and a first win at Augusta since 2005, parred the first four holes and bogeyed the newly-lengthened fifth for the third day running to fall four shots off the pace.