Jordan Spieth's bid for the third leg of an unprecedented calendar grand slam remains firmly on track after a breathless third round of the 144th Open Championship.
But the Masters and US Open champion could be denied a place in the record books by an equally remarkable performance after 22-year-old Irish amateur Paul Dunne claimed a share of the lead at St Andrews.
Days after being mistaken for Spieth by fans seeking autographs due to their identical clothing, Dunne carded a flawless 66 on the Old Course to finish 12 under par alongside playing partner Louis Oosthuizen - who won the 2010 Open at St Andrews - and Australian Jason Day.
Spieth also shot 66 to lie just a shot behind, with 2007 and 2008 champion Padraig Harrington on 10 under after a superb 65.
Nine players were tied for sixth on nine under, including another amateur in American Jordan Niebrugge, Justin Rose, Sergio Garcia and Adam Scott, along with England's Danny Willett, who led outright after 10 holes but drove out of bounds on the 14th.
Spieth is looking to become the first player to win the first three majors of the year and just the third to win any three in a single season - Ben Hogan won the Masters and US Open in 1953 but missed the US PGA to compete in, and win, the following week's Open at Carnoustie, while Tiger Woods won the US Open, Open and US PGA in 2000 and completed the 'Tiger Slam' in the 2001 Masters.
"It hasn't come up in my head while I've been playing yet," said the 21-year-old, who would also replace Rory McIlroy as world number one with victory.
"I can't speak for tomorrow given it's the last round and if I have a chance coming down the stretch, if it creeps in, I'll embrace it. I'll embrace the opportunity that presents itself.
"I don't look at it as a negative thing, I look at it almost as an advantage. Why should it add more pressure in a negative way?
"If it adds more pressure, it just makes me feel like this is something that's a little more special, let's go ahead and get the job done.
"I know it's easier said than done, but when you say added pressure, most people associate that with negativity or something that can hinder what's comfortable.
"For me, I think it could be advantageous. You hit the ball a little bit further, you can really get your mind around a more specific target and block out other things."