Rory McIlroy has demoralised most of his opposition this season but as he enters the final round of the Tour Championship tied for the lead with Billy Horschel, he put his weariness and some scrappy play behind him for a moment to reminded them just why he's the favourite to take the title and the $10m FedEx Cup bonus to boot — experience under the cosh.

"I was three behind going into the back nine at the PGA and I was able to claw it back and win," he told Sky Sports after carding a three under 67 to Horschel's 69 to share top spot on nine under.

"All these experiences of holding on to win at major championships and big events will all stand me in good stead. So hopefully those experiences will help me tomorrow."

If McIlroy is on his A game on Sunday, it's almost certainly game over. But like the Tiger Woods of old, his B game is proving to be good enough so far this week. Just.

"My short game saved me today," he said, reflecting on a particularly important par-save from eight feet at the 11th that kept him within three shots of Horschel, who had gone out in 32 but wobbled on the back nine.

"The putt on 11 was a big putt expecially after  Billy narrowly missed for birdie putt there and me coming off the back of a three-putt on 10. It was important for sure."

McIlroy also three-putted the second from 50 feet as he started birdie-bogey-birdie. And when he did it again at the 10th, failing to take advantage of Horschel's first mistake of the day, it looked as though the tournament might be slipping away.

It's been a long, hard summer winning majors and WGCs, and he was quick to remind the opposition that he really hasn't played at all well yet.

"I felt a little weary coming in this week and by no means have I played my best golf," he said. "I've found it a grind and struggled at times out there but I am tied for the lead going into the last day and I can't ask for any more."

Horschel had been almost faultless until he hit the back nine and suddenly got quick at the top on his tee shots and followed that mistake at the 10th with a bogey at the 13th that allowed McIlroy to close to within two.

The sometimes brash American hit just two fairways on the back nine and his failure to birdie the par-five 15th was costly as McIlroy rolled in a 20 footer for eagle there to draw level having looked like fall four shots behind just four holes earlier.

"The eagle on 15 - I hadn't really played the par-fives well all week and this was a big putt for me," McIlroy said. "It was a big turning point and got me tied for the lead."

The 25-year old from Holywood had his best strut going for the last three holes, trying his best to hit Horschel with some of that moxie Jack Nicklaus loves.

But Horschel was fading of his own accord and McIlroy had enough problems of his own in the end end did well to chip and putt for pars at the 17th and 18th.

It would be tempting to think that it will be a two-horse race on Sunday but with seven other players within five strokes of their lead at 9 under, McIlroy's weariness and Horschel's inexperience at the very top level may well give the chasing bunch a chance.

With the ultimate grinder in former FedEx Cup winner Jim Furyk (67) just two behind and in third oon seven under, it would be ironic if the man who has failed to turn so many 54-hole leads into a win in recent daeason should win for the first time since he claimed the Tour Championship at East Lake in 2010.

Just three behind are Justin Rose (66), Jason Day (70) and Rickie Fowler (67) with Russell Henley (67), Ryan Palmer (69) and Chris Kirk (71) only four behind.

Horschel spoke of his expectant wife and "duking it out with Rory" on Sunday but Furyk was hugely upbeat after his round and could be poised to pounce.

As for the PGA Tour's dream finish, what about this tweet: