Rory McIlroy believes he will need to match his best ever score at Augusta National to stand a chance of winning the Masters after a frustrating third round.

McIlroy got off to the flying start he needed with birdies on the second and third, but three-putted the fifth and seventh, the latter costing him a double bogey after his approach from the trees had plugged in a greenside bunker.

A birdie on the eighth repaired some of the damage and after a good chance went begging on the 11th, McIlroy holed from 20 feet to pick up another shot on the 12th.

However, massive drives on the 13th and 15th resulted in nothing better than par fives and McIlroy had to settle for a 71 to finish level par, six shots behind Ryder Cup team-mates Justin Rose and Sergio Garcia.

"I'm going to need to play probably the round of my life tomorrow to have a chance."

"I had some chances on the back nine that I could have converted," admitted McIlroy, who needs to win the Masters to become the sixth player to complete a career grand slam.

"I had a great chance on 11 and 14. And where I hit my drives on 13 and 15, I should be making birdie off the tee shots. I was just in between clubs on both of those holes and hit the wrong one on both, I guess, and left myself in an awkward position.

"I think I probably could have shot a 67 or 68, but just a few too many wasted opportunities. I'm going to need my best score around here, 65, to have a chance tomorrow.

"But again you can't start going for shots that aren't there. You still need to play smart when you have to. I'll try to take my chances, birdie the par fives and birdie some of the other holes and try to not make too many mistakes.

"I'm going to need to play probably the round of my life tomorrow to have a chance."

In 2011 he shot a seven-under par 65 in the first round, which remains his best score at Augusta.