Rory McIlroy admitted his prospects of completing the career grand slam at the first attempt did not look good ahead of the third round of the 79th Masters on Saturday.
McIlroy recovered from a front nine of 40 at Augusta National to storm home in 31 and card a second consecutive 71 on Friday, but still found himself 12 shots off the record pace set by Jordan Spieth.
The biggest comeback after 36 holes at the Masters was eight shots by Jack Burke in 1956 and McIlroy conceded the respective form of himself and Spieth - who is now 47 under par for his last 14 tournament rounds - made breaking that record unlikely.
“I’m really proud of myself the way I fought back and to shoot five under was a good effort, but I am going to need four more like that it looks like,” the world number one said.
“I would need to shoot a 14-under-par weekend and Jordan would have to play a couple of average rounds, and neither of those two things look like they’re going to happen, so it’s going to be tough.
“I’ll go out and try and play the best that I can and we’ll see where that leaves me.”
On the day that his mentor Ben Crenshaw played his final ever round after 44 consecutive appearances at Augusta National, Spieth added a second round of 66 to his opening 64 to post a total of 130, one shot better than the previous best set by Ray Floyd in 1976.
That also equalled the 36-hole record in any major - shared by Nick Faldo, Brandt Snedeker and Martin Kaymer - and at 14 under is the lowest 36-hole score in relation to par.
“I just need to keep my head down, set a goal for myself,” said Spieth, who held a five-shot lead over Charley Hoffman, with English pair Justin Rose and Paul Casey and Dustin Johnson two shots further back.
“It’s definitely going to be more challenging and I am going to have to be aware of that and be okay with a bogey or two.
“The hardest thing to do is put aside wanting to win so bad and just kind of going through the motions and letting my ball striking and putting happen.
“I got off to a great start and had a chance to win last year on Sunday. I’d like to have that same opportunity this year. Again, this is only the halfway point and I’m aware of that.
“What I learned (last year) was patience. The weekend of a major, those rounds can often seem like two rounds in kind of the mental stuff that’s running through your head, the stress levels.”