A dizzying third round at The Masters with an amazing 16 changes at the top ended with Sweden's Peter Hanson one ahead of Phil Mickelson, while Padraig Harrington remains in contention.
The Dubliner had four birdies in a row from the 13th and added another on the last for a 68. It means he still has a chance of becoming the first player to win the eve-of-tournament par three competition and the event proper four days later.
Rory McIlroy has a disappointing round and sits on one over with Graeme McDowell one shot back on two over par.
Quiet man Hanson had the round of his life, a seven under par 65, and on only his second trip to Augusta will start the final day nine under.
But in a brilliant comeback from an appalling start to the tournament, Mickelson refused to let the 34-year-old, whom he comfortably beat in the singles of the last Ryder Cup, get clean away.
Trying to join Tiger Woods as a four-time winner of the title - Woods is certainly not going to stop him from 38th place on three over - the left-hander had an eagle and four birdies in a back nine 30 that was only one outside the Masters record.
It gave Mickelson, who had been four over after 10 holes of the year's first major, a 66 - only one off his best-ever score in the event.
McIlroy, on the other hand, had a collapse almost as bad as his one on the same course last April.
Having played the back nine then in an horrendous 43 en route to an 80 that took him from four ahead to 10 behind, the 22-year-old US Open champion this time reached the turn in 42 with two double bogeys, including his second of the week on the first, and two bogeys.
When he finally made a birdie on the short 12th and struggling partner Sergio Garcia did the same the pair even shared a hug.
There would be another for the Holywood native on the long 15th and the last - in fact, he almost holed his second shot there - but with a 77 he had fallen all the way from joint third to joint 27th and from one behind to 10 adrift.
Only one player has come from that far back on the final day of a major. Paul Lawrie, still three under here after a 72, was that man in the 1999 Open.
Lee Westwood is going to have to produce something special as well if his 56th attempt to win a major is going to be his first victory.
Runner-up to Mickelson two years ago, Westwood was also one back at halfway, but missed a par putt of little more than a foot on the ninth and had three other bogeys.
Four birdies, though, kept his hopes alive. After a 72 he will tee off again in a tie for sixth on four under.
South Africa's 2010 Open champion Louis Oosthuizen is third at seven under and then come Americans Bubba Watson and Matt Kuchar, but 52-year-old Fred Couples and Jason Dufner, the two halfway leaders, were two more to struggle.
Hanson does not have a single top six finish in any major to his name - his best was seventh in last year's US Open 11 shots behind McIlroy.
But he has four European Tour wins and one of them came in the penultimate event of the last Ryder Cup place and enabled him to take the last automatic spot in Colin Montgomerie's side.
He played with Mickelson in the first two rounds and was just ahead of him in a scintillating Saturday.
"I hear Phil make eagle on the 13th, but it just helps you a little bit to focus," he said, "and you have to make as many birdies as you can."
Hanson admitted, though, it might not be the easiest night he has ever had.
"I think it will be hard, but I'm just going to spend time with the family and get as much sleep as I can."
Mickelson has had an eagle - a curling 25-footer on the 13th to an almighty roar - and 13 birdies since a triple bogey seven on the 10th in his first round.
Mickelson said: "At some point I am going to get hot on this course, but I have to be in a position where it gets me onto the leaderboard.
"My finish on Thursday (two under for the last six for a 74) enabled me to do that.
"My putting has been so good, the best of my career probably."
There were also two shots of pure magic - a parachute chip at the 15th and an iron hooked round the trees onto the final green.
Mickelson had birdied the 18th all three days. He will be hoping he does not have to do it again to be crowned champion for the fourth time in nine years.
Hanson actually started with a bogey, but after birdies at the second, seventh and eight turned in 34 and then picked up five more shots in the last seven - and two in the last two.
Alongside Harrington and Westwood are Hanson's compatriot Henrik Stenson and last week's Houston Open winner Hunter Mahan .