Masters 2015: Rory McIlroy - I need two phenomenal rounds

Rory McIlroy needs to "shoot a 14-under-par weekend" to have a chance of winning the Masters to complete the Grand Slam at his first attempt.

Northern Ireland's world number one is two under at halfway, 12 shots behind America's Jordan Spieth who shot a six-under 66 and leads the field by five.

"I'll need two phenomenal rounds and Jordan would have to play a couple of average rounds," said McIlroy, 25.

"Neither look like they're going to happen, so it's going to be tough."

McIlroy won last year's Open to add to his victories in the US Open and US PGA Championship to put himself on the brink of becoming only the sixth man to complete the Grand Slam of golf's four majors.

He started the Masters as favourite and made a solid start on Thursday but his one-under-par 71 left him seven behind first-round leader Spieth.

Noh Seung-yul, JB Holmes and Ryan Palmer have managed a yard shorter than McIlroy's opening tee shot on day one

It did not get better at the start of his second round as he completed the front nine in 40, leaving him 17 shots off the lead and beyond the projected cut mark of two over.

However, he improved on his second nine, coming home in 31 with four birdies, an eagle and one bogey for a second consecutive 71.

It still leaves McIlroy with an almighty task to challenge for the Green Jacket come Sunday, with 21-year-old Spieth adding a 66 to his first-round 64 to shoot the lowest halfway score in the history of the Masters with 130.

"I'll go out and try and play the best that I can and we'll see where that leaves me," McIlroy added.

"But, with a few more nine holes like the one I just had there, you never know."