Phil Mickelson has a one shot lead over Hunter Mahan, Steve Stricker and Charl Schwartzel, the 42 year old, who interestingly turns 43 tomorrow, recovering from a slow start with a final nine of 32 to lead again after beginning the day in a share of the lead with Billy Horschel.
So many great story lines could potentially unfold in tomorrow's final round.
Mickelson, already a winner of four major championships, looks on target to win the one which will no doubt mean the most to him but within two shots are four players (Mahan, Stricker, Justin Rose and Luke Donald ) who have for some time now been considered amongst the game's best players without a major title to their name.
Another of the game's best in recent years, Schwartzel, who is looking to add this title to his Masters victory of 2011, is just one from the lead and within four of Mickelson are some of the game's potentially great emerging players such as Billy Horschel, Jason Day and Rickie Fowler.
When round two was completed earlier in the day, Mickelson led along with Billy Horschel at 1 under and as he, Donald and Horschel set out at 2.40pm the event was back on schedule and with conditions again perfect several players made early moves.
With Mickelson dropping two shots early it was Schwartzel however who established a lead when he reached the turn in 34 and at 2 under led over Donald.
Mickelson began his fightback with birdies at the 10th and 11th and went agonisingly close with beautiful birdie putts on 15 and 16 that refused to drop. When he reached the 17th tee he was one behind Donald who had taken the lead with two birdies through the turn.
Mickelson hit a superb 4 iron to 12 feet from 254 yards and when he had holed that and Donald bogeyed, the two shot swing had Mickelson one ahead of Donald and Schwartzel.
The closing few holes of Merion claimed several victims late in the day. Donald dropped three shots over the final two holes, while Mahan, Schwartzel and Rose all dropped shots at the 17th and 18th.
Mickelson too would bogey the last but he had done enough to hold the lead and head into tomorrow's final round with the prospect of a very emotional and deserved victory ahead of him.
"It's going to be a fun day tomorrow," said Mickelson. "I'm really looking forward to it I'm looking forward to facing the challenge of Merion again. It's a wonderful test.
"I think that there are holes that are obviously very difficult pars, some of the hardest par holes that we have ever played. But we have also have a number of birdie opportunities, much more so than in years past. So there's a great mixture of holes and it's been fun to test ourselves."
Mickelson was still enthusing over the 4 iron to the 17th when interviewed after his round. "The 4 iron I hit - I just stood there and admired it, it was one of the best shots I've ever hit. I mean it just was right down the centre of the green and I was hoping it would kind of get the right bounces and so forth and it did. It left me a beautiful uphill putt that I could be aggressive with and I made it. And it was that was fun to do that because that's just not a hole you expect to get one back."
Mickelson was also excited about the prospect of the final round. "I love being in the thick of it. I've had opportunities in years past, and it has been so fun, even though it's been heart breaking to come so close a number of times and let it slide. But I feel better equipped than I have ever felt heading into the final round of a U.S. Open. My ball striking is better than it's ever been. My putting is better than it has been in years, and I feel very comfortable on this golf course. I love it.
"I have the opportunity to play with a friend of mine, Hunter Mahan, and his caddie Woody is great friend of Bones and I and it should be a fun day."
"At 43 (tomorrow) I feel as good as I've ever felt. I feel like I'm in better shape than I've been in years. I feel stronger than I've been, more flexible. And I've had no injuries or aches or pains.
"I've changed a lot of things since I have been diagnosed with psoriatic arthritis. I changed my diet, I changed the way I do things. But I feel terrific and I don't think that my golf swing, which is not predicated on violence and rotation and so forth, it's developed more on length and arc and leverage to create speed as opposed to physical brute force, has allowed me to play injury free for this many years. My body feels great.
"It (tomorrow) has got the makings to be something special, but I still have to go out and perform and play some of my best golf."
Jason Day produced the second best round of the day (68) to lead the Australians at 2 over and just three from the lead. Day has already shown with his runner-up finishes in this event and the Masters along with a 3rd place finish at the Masters that the big stage holds no real fears.
Day confirmed just that soon after he walked from the course today. "Really, the majors are kind of where it's at. I think that it really defines a career and if you can win as many as you can. It just goes to show, I mean, you're playing against the best players in the world at the highest level on the toughest golf course, courses, and I think that I just really enjoy playing in front of a lot of people and playing against the best.
"I think that Australian golf is in good shape right now, especially with how everyone's playing. Goggin and Senden this week are playing great. It would mean the world to me if I could win my first Major here. I've had a couple of opportunities to win before, but to actually win on I think one of the toughest U.S. Opens that I've ever played. I only played three, but from looking at the past I think this is one of the toughest U.S. Opens I've ever seen. To know that my game is good enough to compete and win out here on this golf course would be great."
Another 68 from Day tomorrow might just see him holding the US Open trophy two months after his fellow Queenslander Adam Scott won the Masters.
John Senden contended early on day three with birdies at his opening two holes but dropped six shots in his last twelve holes and finds himself six shots from Mickelson's lead in 11th position.